Question

A sample of 15 litres of mixture of a paint and thinner is found to have 20 %thinner. Find how much pure paint should be added to bring down the percentage of thinner to 10 %.​

Answer 1

the amount of thinner in the sample is 20%

20% of 15 litre =

$\frac{20}{100} \times 15 = 3$

3 litre of thinner is thier

and rest of the sample is paint = 15- 3 = 12 litre

to make 10% of x amount of thinner as 3 litre,

$\frac{10}{100} \times x = 3 \\ x = \frac{3 \times 100}{10} \\ x = 30$

so 30 litres of sample will be made to 10% the amount of 3 litre thinner.

and the rest is paint = 30 - 3 = 27 litre

(27 - 12 =) 15 litre of paint should be added.