John, Jack, and Jill have 159 marbles altogether. John has 2 more marbles than Jack, and if Jill gave 5 marbles to Jack, Jack would have the same number of marbles as Jill. How many marbles does each of them have?

Answers

Answer 1

Answer:

someone else tell me to thank you


Related Questions

Find the radius of a circle in which the central angle, a, intercepts an arc of the given length s.
a = 60°, s = 44 ft
The radius is ft.
(Round to the nearest hundredth as needed.)

Answers

Answer:

42.02 ft

Step-by-step explanation:

60 : 360 = 44 : x

x = 264 ft (length of the circumference)

C = 2 * radius * pi

radius = C / 2 * pi

Radius = 264 / 2 * pi = 42,016905 ft

Passion wants to rent a car to take a trip and has a budget of $75. There is a fixed rental fee of $25 and a daily fee of $10. Write ab inequality that would be used to solve for the maximum number of days for which passion can rent the car on her budget

Answers

Answer:

5 days

Step-by-step explanation:

75 = 10d +25

-25           -25

50 = 10d

/           /

10        10

5 = d

Solve this proportion mentally by scaling up or scaling down.

Answers

Answer: 63 miles

Step-by-step explanation: 21 miles x 3 = 63 miles

you times it by 3 because to get 3 gallons to 9 gallons, you have to multiply it by 3

2. Kayli swam 0.7 kilometers at the school swimming pool. How many meters did she swim?
Kayli swam
meters in the swimming pool.



Answers

Answer:

To convert kilometres to metres, divide the value by 1000.

0.7 ÷ 1000 = 700 metres

Kayli swam 700 meters in the swimming pool

Hope this helps!

What is the solution set to this equation? Log2(x - 2) + log2x = 3

Answers

the solution set is answer A.

The required, solution set to the given equation is {4}. Option A is correct.

What are logarithmic functions?

A logarithmic function is a mathematical function that represents the logarithm of a number with respect to a given base. In other words, it is a function that relates a number to its logarithm. The general form of a logarithmic function is f(x) = logₐ(x).

Using the product rule of logarithms, we can combine the two logarithms on the left-hand side of the equation:

log2(x - 2) + log2x = log2[(x - 2) * x] = log2(x² - 2x)

So the given equation becomes:

log2(x² - 2x) = 3

2³ = x² - 2x

8 = x² - 2x

x² - 2x - 8 = 0

Factor this quadratic equation as:

(x - 4)(x + 2) = 0

x - 4 = 0, which gives x = 4

x + 2 = 0, which gives x = -2

However, the logarithm function is only defined for positive values of x, so the only possible solution is:

x = 4

Therefore, the solution set to the given equation is {4}.

Learn more about logarithmic function here:

https://brainly.com/question/30284289

#SPJ2

Half of a set of the parts are manufactured by machine A and half by machine B. Six percent of all the parts are defective. Three percent of the parts manufactured on machine Are defective. Find the probability that a part was manufactured on machine A, given that the part is defective. (Round your answer to 4 decimal places.) Probability

Answers

Answer:

0.25 = 25% probability that a part was manufactured on machine A, given that the part is defective.

Step-by-step explanation:

Conditional Probability

We use the conditional probability formula to solve this question. It is

[tex]P(B|A) = \frac{P(A \cap B)}{P(A)}[/tex]

In which

P(B|A) is the probability of event B happening, given that A happened.

[tex]P(A \cap B)[/tex] is the probability of both A and B happening.

P(A) is the probability of A happening.

In this question:

Event A: Defective

Event B: Manufactured by machine A.

Six percent of all the parts are defective.

This means that [tex]P(A) = 0.06[/tex]

Probability that a part is defective and was manufactured on machine A

3% of the parts manufactured on machine A are defective, manufacture A is responsible for 50% of the parts. So

[tex]P(A \cap B) = 0.03*0.5 = 0.015[/tex]

Find the probability that a part was manufactured on machine A, given that the part is defective.

[tex]P(B|A) = \frac{P(A \cap B)}{P(A)} = \frac{0.015}{0.06} = 0.25[/tex]

0.25 = 25% probability that a part was manufactured on machine A, given that the part is defective.

Find the equation of a line parallel to y'= -8x+6.

Answers

Answer:

The equation must include -8 as the slope

Step-by-step explanation:

Hi there!

Two key points to keep in mind:

Linear equations are typically organized in slope-intercept form: [tex]y=mx+b[/tex] where m is the slope and b is the y-intercept (the value of y when x is 0).Parallel lines always have equal slopes

Given the equation y=-8x+6, we can identify that -8 is in the place of m in y=mx+b, making it the slope.

For a line to be parallel to y=-8x+6, it would have to have a slope of -8 as well. This is the only quality a line needs to be parallel to this given line.

I hope this helps!

a and b are complementary angles and a and c are supplementary angles. If a=xº, (a) express b and c in terms of x
(b) find c - b.​

Answers

Step-by-step explanation:

a + b = 90

a + c = 180

a) If a = x, the. we can write

x + b = 90 and x + c = 180

or

b = 90 - x

c = 180 - x

b) c - b = (180 - x) - (90 - x)

= 180 - x - 90 + x

= 90

(x) 3 5 7
(y) 7 11 15

Find x, when y = 21

Answers

Answer:

x = 10

Step-by-step explanation:

y = 2x + 1

21 = 2x + 1

21 - 1 = 2x

2x = 20

x = 10

find the inverse function of F(x) = 1/2x-6​

Answers

F^-1 (x) = 2x + 12 hope it help

Answer:

[tex]F^{-1} (x) = 2x + 12[/tex]

Step-by-step explanation:

Let's assume F(x) = y, then

[tex]y = \frac{1}{2} x - 6[/tex]

Let us solve the equation for x.

[tex]y + 6 = \frac{1}{2} x[/tex]

[tex]2y + 12 = x[/tex]

Next, replace y with x and also replace x with F⁻¹(x)

Answer: [tex]F^{-1} (x) = 2x + 12[/tex]

Which graph shows the solution to this system of inequalities?
y>-1/3x+1
y>2x-3

Answers

Given:

The system of inequalities is:

[tex]y>-\dfrac{1}{3}x+1[/tex]

[tex]y>2x-3[/tex]

To find:

The graph of the given system of inequalities.

Solution:

We have,

[tex]y>-\dfrac{1}{3}x+1[/tex]

[tex]y>2x-3[/tex]

The related equations are:

[tex]y=-\dfrac{1}{3}x+1[/tex]

[tex]y=2x-3[/tex]

Table of values for the given equations is:

    [tex]x[/tex]                   [tex]y=-\dfrac{1}{3}x+1[/tex]             [tex]y=2x-3[/tex]

   0                             1                              -3

   3                             0                              3

Plot (0,1) and (3,0) and connect them by a straight line to get the graph of [tex]y=-\dfrac{1}{3}x+1[/tex].

Similarly, plot (0,-3) and (3,3) and connect them by a straight line to get the graph of [tex]y=2x-3[/tex].

The signs of both inequalities are ">". So, the boundary line is a dotted line and the shaded region or each inequality lie above the boundary line.

Therefore, the graph of the given system of inequalities is shown below.

Given the functions below, find (g•h) (1).
g(x) = х^2 +4+ 2х
h(x) = — 3х + 2
-7
-30
35
7

Answers

Answer:

-7

Step-by-step explanation:

We are given the following functions:

[tex]g(x) = x^2 + 4 + 2x[/tex]

[tex]h(x) = -3x + 2[/tex]

(g•h) (1)

The multiplication is:

[tex](g \times h)(1) = g(1) \times h(1)[/tex]

So

[tex]g(x) = 1^2 + 4 + 2(1) = 7[/tex]

[tex]h(1) = -3(1) + 2 = -3 + 2 = -1[/tex]

Then

[tex]g(1) \times h(1) = 7(-1) = -7[/tex]

So -7 is the answer.

PLS HELPP MEE !!
Use a calculator to find the r-value of these data. Round the value to three decimal places.

Answers

The Answer is -0.985

I just took the test.

A table is made using the following two patterns.
Pattern 3: Starting number: 5, Rule: add 1
Pattern y: Starting number: 10, Rule: add 2
Complete the table for the given patterns.

Answers

Answer:

x = 6, y = 12

x = 7  y = 14

Step-by-step explanation:

im pretty sure that right, hope this helps!

a)Loss is denoted by a negative integer and profit is denoted by a positive integer. A
cement company earns a profit of ₹ 10 per bag of white cement and a loss of ₹ 5 per
bag of grey cement. The company sells 325 bags of white cement and 500 bags of
grey cement. What is its profit or loss?

Answers

Answer:

There was a profit of ₹750.

Step-by-step explanation:

325 bags of white cement

Profit of 10 for each bag of white cement. So

[tex]P = 325*10 = 3250[/tex]

500 bags of grey cement.

Loss of 5 for each bag of grey cement. So

[tex]L = 5*500 = 2500[/tex]

What is its profit or loss?

3250 - 2500 = 750

Positive, so profit. There was a profit of ₹750.

guys plz help i’m struggling

Answers

Answer:

0.46017

Step-by-step explanation:

Given :

Mean score = 75

Standard deviation, s = 10

Areum's score = 76

Probability of scoring higher than Areum is given by :

P(x > 76)

The standardized score : (x - mean) / standard deviation

P(x > 76) = P[Z > (76 - 75) / 10]

P[(Z > 0.1)] = 0.46017 (Z probability calculator)

= 0.46017

The diameter of a pipe is normally distributed, with a mean of 0.8 inch and a variance of 0.0025. What is the probability that the diameter of a randomly selected pipe will exceed 0.9 inch?

Answers

Answer:

0.02275

Step-by-step explanation:

Standard deviation is the square root of variance

Standard deviation= Square(0.0025)= 0.05

Because of the normally distributed, the z- score for 0.9 inches is:

(0.9-0.8)/0.05= 2

-> P(x<= 0.9)= P(2) = 0.97725

-> P (x>= 0.9)= 1-0.97725 = 0.02275

The following data represent the maximum wind speed (in knots) and atmospheric pressure (in millibars) for a random sample of hurricanes that originated in the Atlantic Ocean.

Atmospheric Pressure (mb) Wind Speed (knots) Atmospheric Pressure (mb) Wind Speed (knots)
993 50 1006 40
995 60 942 120
994 60 1002 40

Required:
a. Find the y-intercept of the least-squares regression line, treating atmospheric pressure as the explanatory variable (round to four decimal places.)
b. Find the slope of the least-squares regression line, treating atmospheric pressure as the explanatory variable (round to four decimal places.)
c. Is it reasonable to interpret the y-intercept of the least-squares regression line, treating atmospheric pressure as the explanatory variable? Why or why not?

Answers

Answer:

Step-by-step explanation:

X                  Y                 X²                              Y²                  XY

993              50               986049                 2500              49650

995              60               990025                 3600              59700

994              60               988036                  3600              59640

1006             40               1012036                 1600              40240

942             120               887364                 14400              113040

1002             40               1004004                 1600              40080

[tex]\sum X: 5932[/tex]   [tex]\sum Y : 370[/tex]     [tex]\sum X^2 : 5867514[/tex]    [tex]\sum Y^2 = 27300[/tex]    [tex]\sum XY : 362350[/tex]

To determine the regression:

[tex]Mean \ (X) = \dfrac{\sum X }{n} \\ \\ = \dfrac{5932}{6} \\ \\ = 988.67[/tex]

[tex]Mean \ (Y) = \dfrac{\sum Y}{n} \\ \\ = \dfrac{370}{6} \\ \\ = 61.67[/tex]

Intercept [tex]b_o = \dfrac{\sum YX *\sum X^2 - \sum X \sum Y}{n(\sum X^2) - (\sum X)^2}[/tex]

[tex]=\dfrac{370(5867514) -(5932)(370)}{6(5867514) - (5932)^2}[/tex]

= 131760.9563

Slope [tex]b_1 = \dfrac{n(\sum XY) -(\sum X *\sum Y) }{n(\sum X^2)-(\sum X)^2}[/tex]

[tex]b_1 = \dfrac{6(362350) -(5932*370) }{6(5867514)-(5932)^2}[/tex]

[tex]b_1 = -1.2600[/tex]

The regression line equation [tex]Y = b_o +b_1X[/tex]

[tex]Y = 131760.96 -1.2600 X[/tex]

We then make a comparison of the slope of the equation to y = mx+c

slope of the equation = -1.2600

the y-intercept corresponds to when X = 0, thus:

y-intercept = 131760.9563

Yes, it is reasonable to interpret the y-intercept of the regression line, Using atmospheric pressure as an explanatory variable due to the fact that:

X is the independent variable and Y exists as the dependent variable.

Please answer my question correctly.

Nonsense/Plagiarized = Report​

Answers

so the circumference of a circle is C=2 times pi times the radius. in this case it would be C= 2(pi)(4) which is 25.1 :)
Problem:-

Find the perimeter or circumference and area of each figure. Round to the nearest tenth.

Solution:-

The circumference of a circle with radius r is given by C = 2πr. The radius of the circle is 4 in.

Substitute 4 for r.

[tex]\sf{C=2πr}[/tex]

[tex]\sf{ \: \: \: \: =2π(4)}[/tex]

[tex]\sf{ \: \: \: \: ≈{\color{darkviolet}{25.1}}}[/tex]

Answer:-

The circumference of the circle is about 25.1 in.

======================

The area of a circle with radius r is given by A = πr².

Substitute 4 for r.

[tex]\sf{A = πr²}[/tex]

[tex]\sf{ \: \: \: \: = π(4)²}[/tex]

[tex]\sf{ \: \: \: \: ≈{\color{magenta}{50.3}}}[/tex]

Answer:-

The area of the circle is about 50.3 in².

======================

#Hope it helps!

(ノ^_^)ノ

A man takes a 375-mile trip to Miami. His large car gets 18 miles per gallon, and his small car gets 32 miles
per gallon. How many gallons of gas will he save if he takes the smaller car?

Answers

Answer: 9 gallons

Step-by-step explanation:

How many gallons needed for small car: 375/32 = 11.7 or 12

How many gallons for large car: 375/18 = 20.8 or 21

21-12 = 9

Write the coordinates as an ordered pair for any point that is a solution to the of inequality graphed below.


Answers

Answer:

The inequality that represents the graph must have the following form:

[tex]y > -4\cdot x + 6[/tex]

Step-by-step explanation:

First, we need to determine the equation of the line which represents the "lower" bound of the inequality:

[tex]y = m\cdot x + b[/tex] (1)

Where:

[tex]x[/tex] - Independent variable, horizontal axis.

[tex]y[/tex] - Dependent variable, vertical axis.

[tex]m[/tex] - Slope.

[tex]b[/tex] - Intercept.

Given two distinct points of the line, we can solve for both slope and intercept: [tex](x_{1}, y_{1}) = (1, 2)[/tex], [tex](x_{2}, y_{2}) = (0, 6)[/tex]

[tex]m + b = 2[/tex] (2)

[tex]b = 6[/tex] (3)

The solution of the system is: [tex]m = -4[/tex], [tex]b = 6[/tex]

Then, the inequation must have the following form:

[tex]y > -4\cdot x + 6[/tex]

attendance drop at 7% this year to 1050 what was the attendance before the drop

Answers

Answer:

7% divided by 1050 is basically 73.5 but the fraction of that is 147/2 hope u find my answer reasonable have a great day.

Step-by-step explanation:

Payment types vary at the grocery store. Here are the proportions of the leading three payment methods: Payment Method Cash Credit Cards Debit Cards Proportion 0.11 0.43 0.21 If a transaction is selected at random, the probability that the customer did not pay with a Debit Card is .

Answers

Answer:

0.79

Step-by-step explanation:

Given the probability distribution :

Payment Methd: Cash Credit Cards Debit Cards Proportion : ____0.11 ____ 0.43 _____0.21

The probability that a customer did not pay with debit card can be obtained as :

If customer did not pay with debit card, then he would have paid with any of the other payment methods

This Can best be obtained using the complement method

P(not debit card) = 1 - P(debit card)

P(debit card) = 0.21

P(not debit card) = 1 - 0.21

P(not debit card) = 0.79

i already have A but I do not have B

Answers

Answer:

-4 , -1 , -2 , 0 , +1 , +3

Step-by-step explanation:

Answer:

the integers -4,-2,-1,0, +1, +3

Step-by-step explanation:

because when you put them in order  you find which pairs are located between -5 and +5

-8,-4,-2,-1,0,+3,+8,+9

which tells you that

-4,-2,-1,0, +1, +3 are between -5 and +5

A phone manufacturer wants to compete in the touch screen phone market. He understands that the lead product has a battery life of just 5 hours. The manufacturer claims that while the new touch screen phone is more expensive, its battery life is more than twice as long as that of the leading product. In order to test the claim, a researcher samples 45 units of the new phone and finds that the sample battery life averages 10.5 hours with a sample standard deviation of 1.8 hours.a. Select the relevant null and the alternative hypotheses. b-1. Calculate the value of the test statistic.b-2. Find the p-value.

Answers

Answer:

a)

The null hypothesis is [tex]H_0: \mu \leq 10[/tex]

The alternative hypothesis is [tex]H_1: \mu > 10[/tex]

b-1) The value of the test statistic is t = 1.86.

b-2) The p-value is of 0.0348.

Step-by-step explanation:

Question a:

Test if the battery life is more than twice of 5 hours:

Twice of 5 hours = 5*2 = 10 hours.

At the null hypothesis, we test if the battery life is of 10 hours or less, than is:

[tex]H_0: \mu \leq 10[/tex]

At the alternative hypothesis, we test if the battery life is of more than 10 hours, that is:

[tex]H_1: \mu > 10[/tex]

b-1. Calculate the value of the test statistic.

The test statistic is:

We have the standard deviation for the sample, so the t-distribution is used to solve this question

[tex]t = \frac{X - \mu}{\frac{s}{\sqrt{n}}}[/tex]

In which X is the sample mean, [tex]\mu[/tex] is the value tested at the null hypothesis, s is the standard deviation and n is the size of the sample.

10 is tested at the null hypothesis:

This means that [tex]\mu = 10[/tex]

In order to test the claim, a researcher samples 45 units of the new phone and finds that the sample battery life averages 10.5 hours with a sample standard deviation of 1.8 hours.

This means that [tex]n = 45, X = 10.5, s = 1.8[/tex]

Then

[tex]t = \frac{X - \mu}{\frac{s}{\sqrt{n}}}[/tex]

[tex]t = \frac{10.5 - 10}{\frac{1.8}{\sqrt{45}}}[/tex]

[tex]t = 1.86[/tex]

The value of the test statistic is t = 1.86.

b-2. Find the p-value.

Testing if the mean is more than a value, so a right-tailed test.

Sample of 45, so 45 - 1 = 44 degrees of freedom.

Test statistic t = 1.86.

Using a t-distribution calculator, the p-value is of 0.0348.

a housewife spent 3/7 of her money to buy yams and 1/2 of the remainder to buy rice what is the fraction of her money left​

Answers

Answer:

Fraction of money spent on calculator = 2/5

Find the fraction of money left:

1 - 2/5 = 3/5

Find the fraction of money spent on a book:

4/7 x 3/5 = 12/35

Answer: She spent 12/35 of the money on a book

------------------------------------------------------------------------------------------------

To find the fraction of saving:

Fraction of money saved = 1 - calculator - book

Fraction of money saved = 1 - 2/5 - 12/35 = 9/35

Fraction of the money saved = 9/35

Step-by-step explanation:

A Little League baseball coach wants to know if his team is representative of other teams in scoring runs. Nationally, the average number of runs scored by a Little League team in a game is 5.7. He chooses five games at random and finds the mean number of runs scored is 7.4 with a sample standard deviation of 2.88.

Required:
Is it likely that his team's scores is different than the national average?

Answers

Answer:

That result implies that t(s) is in the acceptance region for H₀ then we accept H₀, there is not statistics difference between the LL team and the national average

Step-by-step explanation:

The National average number of runs scored by a LL team is

μ   =  5.7

Sample Information:

size sample   n = 5

sample average   x  =  7.4

sample standard deviation    s  =  2.88

Is required to investigate if  that sample average is statistically different from the National average

We will do a test with 95 % of confidence Interval that means

significance level α = 5 %   or α = 0.05.

The sample size is 5 then even when we assume normal distribution the sample size indicates that we need to use t-student distribution. Furthermore, as the question is if the sample average is different from the national the test will be a two-tail test.

Then  α = 0.05    α/2  =  0.025

df  =  n  -  1     df  =  5  -  1     df  =  4

Then from t-student table we get  t(c)  =  2.132

Hypothesis test:

Null Hypothesis                                  H₀              x  =  μ

Alternative Hypothesis                      Hₐ              x  ≠  μ

To calculate t (s)

t(s)  = ( x  -   μ ) / s/√n

t(s)  = ( 7.4  -  5.7  )* 2.24 / 2.88

t(s)  =  1.7* 2.24 / 2.88

t(s)  = 1.32

Comparing  t(s)  and  t(c)

1.32 < 2.132

That result implies that t(s) is in the acceptance region for H₀ then we accept H₀, there is not statistics difference between the LL team and the national average

Evaluate the given equation for the indicated function values. pls help

Answers

Answer:

The answer in each numeral is:

f(4) = 28f(10) = -19f(-5) = -33f(9) = -9

Step-by-step explanation:

To obtain the result in each case, you must replace the variable (n) by the value that appears in the second case, I'll explain it with the first exercise:

1. f(n) = 5n + 8   f(4) = ?

As you can see, in the second doesn't appear f(n), but f(4), that means you must replace the "n" in the equation by 4, if we do this, we obtain:

1. f(4) = 5*(4) + 8f(4) = 20 + 8f(4) = 28

The first answer is 28, now we'll continue with the next exercises:

2. f(n) = -2n + 1f(10) = -2*(10) + 1f(10) = -20 + 1f(10) = -19

3. f(n) = 6n - 3f(-5) = 6*(-5) - 3f(-5) = -30 - 3f(-5) = -33

4. f(n) = -nf(9) = -9

In this form, you can prove the answers are: 28, -19, -33, and -9 respectively.

Answer the following and round to one decimal place.

Answers

Step-by-step explanation:

5 1/2% = 5.5% = 5.5/100 = 0.055

0.055 * 68 = 3.74

Answer:

3.74

Step-by-step explanation:

[tex]5\frac{1}{2}%[/tex] of 68

In order to do this you need to convert 5 1/2 into a decimal!

Answer: 5.5

Explanation: 5 is a whole number and half of one unit will be 0.5

5 + 0.5 = 5.5

Then multiply 5.5 and convert 68 into "0.68"

5.5 × 0.68 = 3.74

Answer: 3.74

Please help please reply

Answers

Answer:

hypotenuse:15

Step-by-step explanation:

Pythagorean Theorem is a^2 + b^2 = c^2

"a" and "b" are the legs, "c" is the hypotenuse

9^2 + 12^2 = 225

[tex]\sqrt{225\\[/tex]

hypotenuse = 15

Other Questions
Scenario: Your parents are out of town for the weekend and you are left home alone. Your bf/gf invites themselves over for a sleepover, your parents will never know. In the space below respond with what you would say to get out of the situation, demonstrating your refusal skills. Divide. Round to the nearest tenth.104 divided by 1.5 Consider a student loan of 15,000 at a fixed APR of 9% for 25 years. A) Calculate the monthly payment B) Determine the tiaras amount paid over the term of the loan C) Of the total amount paid, what percentage is paid toward the principal and what percentage is paid for interest. mention kinds of trips? what is the cube root of 7 How to create an equation for function m? I wrote the right equation as a guess, but I don't understand it. What kind of plot do you prefer in the stories you read and watch?a plot that is grounded firmly in realitya romantic plot that runs wild with imaginationa plot that is sometimes real and sometimes romantic 19. Which of the following statements about HIV is true?A. It attacks the body's immune system so that it cannot effectively fight off infections.B. It does not affect the person until it turns into AIDS.C. It causes cancer.D. None of these choices are correct. if the coordinates of a point p(m-3,-6)=p(-7,-6), then find the value of m The 89 bus comes every 8 minutes. The 368 bus comes every 12 minutes. Both buses are at the same stop at 9 am. At what time will they be at the same stop. Define the term: 1.Respiration 2.Transportation Please help on number 15 thank you! what must happen in order for an ecosystem to survive give any two characteristic of protozoan Political cartoons are also calledstatement cartoonseditorial cartoonsdebate cartoonsnewsworthy cartoons Find the missing dimensions Sean and Tommy are debating the positive and negative impacts of technology on environmental quality. Tommy is listing the negative impacts. Which of the following would help his argument? A. Solar panels have become more effective due to technological improvements. B. Technology has helped make recycling to be more efficient. C. It has created new ways to clean up oil spills. D. Factories contribute to air and water pollution DOWN1. How do we call People who are found in the ice-capes? Change the following sentences into active volce.Social media tears down communication and distance barriers A machine has mechanical advantage 2.What does that mean