A parent has washed some nappies in a strong bleach solution and wishes to rinse them so that they contain as weak a bleach solution as possible. By wringing out, the nappies can be made to contain just half a litre of solution. Show that two thorough rinses, such that the solution strength is uniform, the first using 12 litres of water and the second using 8 litres of water, reduces the strength of the
1 425
If 20 litres of clean water is all that is available and the parent is prepared to do only two rinses, how best should the water be divided between the two rinses?

Answer:

a) Two thorough rinses gives;

1/25 × 1/2 × 2/17 strong bleach/L = 1/425 strong bleach/L

b) The water should be divided into two quantities of 10 liters each

Step-by-step explanation:

The given parameters are;

The initial volume of strong bleach solution in the nappies = 1/2 Liters

The volume of water first used to rinse = 12 liters

The volume of water used in the second rinse = 8 liters

Therefore, we have;

The total volume of the water and the concentrated bleach in the first rinse = 1/2 + 12 = 12.5 Liters

The new concentration of the bleach in the first rinse water = (1/2 strong bleach)/12.5 L = (1/2 strong bleach)/25/2 L = 1/2×2/25 = 1/25 strong bleach/L

The volume of the first rinse introduced in the second rinse = 1/2 Liters

The concentration of the bleach introduced in the second rinse = The new concentration of the bleach in the first rinse water = 1/25 strong bleach/L

The volume of water added in the second rinse = 8 liters

The total volume of the water and the bleach in the second rinse = (8 + 1/2) liters = 8.5 liters

The concentration of bleach in the second rinse = (The concentration of the bleach introduced in the second rinse × (Volume of bleach solution introduced in the second rinse))/(The total volume of the water and the bleach in the second rinse)

The concentration of bleach in the second rinse = (1/25 strong bleach/L × 1/2 L)/(8.5 Liters)

The concentration of bleach in the second rinse = (1/25 strong bleach/L × 1/2 L)/(17/2 Liters) = 1/25 × 1/2 × 2/17 strong bleach/L = 1/425 strong bleach/L

b) The the quantity of water in the first rinse = x

The amount of water in the second rinse = 20 - x

The concentration of bleach in the first rinse = 1/2/(x + 1/2) = 1/(2·x + 1)

The concentration introduced in the second rinse = 1/2 × 1/(2·x + 1) = 1/(4·x + 2)

The total volume of water and bleach introduced in the second rinse = (20 - x + 1/2) = 20.5 - x

The concentration of bleach in the second rinse = 1/(4·x + 2)/(20.5 - x)

The minimum value for the concentration can be found from taking the derivative of the function for the concentration and equation to zero as follows;

[tex]\dfrac{\mathrm{d} \dfrac{1}{\left ( 4\cdot x + 2 \right )\cdot \left ( 20.5 - x \right )}}{\mathrm{d} x} = \dfrac{2\cdot \left ( x - 10 \right )}{\left ( 2\cdot x + 1 \right )^{2}\cdot \left ( 20.5 - x \right )^{2}} = 0[/tex]

2·(x - 10) = 0

x = 0/2 + 10 = 10

x = 10

The the quantity of water in the first rinse = x = 10 liters

The the quantity of water in the first rinse = 10 liters

The amount of water in the second rinse = 20 - x = 20 - x = 20 - 10 = 10 liters

The amount of water in the second rinse = 10 liters

The water should be divided into two quantities of 10 liters each

Therefore, the water should be divided into two quantities of 10 liters each to give a final bleach solution concentration of 1/(4·x + 2)/(20.5 - x) = 1/(4×10 + 2)/(20.5 - 10) = 1/42 × 1/10.5 = 1/441 concentration/liter.

Answer: a) Two thorough rinses gives;

1/25 × 1/2 × 2/17 strong bleach/L = 1/425 strong bleach/L

b) The water should be divided into two quantities of 10 liters each

write an equation of a line passing through point p(-2, 6) that is parallel to the line x= -5​

Luke is a dog walker. He gets $10 per day for walking his neighbor's dogs. He recently snapped his surfboard and wants to buy a used surfboard for $325. If he has $142 in the bank, how many days will he have to walk the dogs to earn enough for the board?

two solutions to the inequality p ≤ 16.

Donte simplified the expression below. 4 (1 + 3 i) minus (8 minus 5 i). 4 + 3 i minus 8 + 5 i. Negative 4 + 8 i. What mistake did Donte make?

Given the points: (-2, 0) and (4,8) find the slope

Hi if you can answer this i'll mark u brainllest and give you MORE points
What are three equivalent decimals for the number -4.2323?

Choose the correct written expression for: (9 x 4) divided by 6.

Options:

he quotient of 9 and 4 times 6

divided by the product of 9 and 4

the product of 9 and 4 divided by 6

9 times 4 divided by 6

Lauren's vet commented that her puppy gained 10% in weight since the first visit. Write an expression that could be evaluated to show the puppy's current weight. Use a variable to represent the weight of the puppy at the first visit. Write the expression in simplified form. If the puppy gains another 10% in weight from the current visit to a future visit, how much will the puppy weigh? Write an expression that could be evaluated to show the puppy's future weight. Write the expression in simplified form.

Raza works at a flea market selling sunglasses. He is paid $7.50/h plus a 75¢ commission for every pair of sunglasses he sells.
Write an equation to model Raza’s earnings. (1 mark)


Find Raza’s earnings if he sells 25 pairs of sunglasses during a 6-h shift. (2 marks)




How many pairs of sunglasses must he sell to earn $90 in 8 h? (2 marks)

Please help it’s graded and I just don’t want to fail

· Evaluate f(2a + b), where f(x) = 4x2 – 3x.​

The point (3,5) has been translated three right and three down. What are
the coordinates of the image?

If you can finish this sentence and get it right you be brainliest

"I can show you the _____ shining, shimmering, splendid"

simplify into one fraction (thanks in advance)

[tex] \frac{2}{p + 3} - \frac{5p}{2p - 2} [/tex]



​

PLEASE ANSWER QUICK leggings are 54.95 they are 30% off how much are they?

Round 0.00208815 to 3 significant figures

How do you write -4.50 as a mixed number

A certain hybrid car can travel 1 4/11 times as far as a similar nonhybrid car can, each one gallon of gasoline. If the nonhybrid car can travel 33 miles per gallon of gasoline, how far can the hybrid travel on 4/5 gallon of gasoline?

Helpppppppppp Meeeeeeeeeee Plssssssssss Problemmm 3

3*a*2*b what is the answer

what is coefficient of x in Y^2x+y

a point is ____
•imaginary
•real

when solving the equation x3 = 22.

Solve and prove the solution for the equation -2(1-4x)=3x+8.

Jose paid 47.00 for 4 movie tickets. Each ticket costs the same amount.what was the cost of each movie ticket in dollars and cents

Which graph is correct for the given equation: Y=-1/4x-4?

Objects that are in the same plane are called _______________ . *

look at image..........................

Which fraction is equivalent to 7/8 ?

A jet ski company charges a flat fee of $22.00 plus $3.00 per hour to rent a jet ski. Another company charges a fee of $17.50 plus $3.75 per hour to rent the same jet ski. Write a system of equations that can be used to determine when the cost will be the same, then solve your system.