Question

20 litres of mixture of acid and water contain 10% water. How much water should be added so that percentage of water becomes 20% in this mixture?

Answer 1

Answer : 2.5 litre

Solution :
_________

Given that : 20 litre of mixture of acid and water contains 10% water.

Then quantity of water :

$20 \times \frac{10}{100} = 2 \: litre$

It means quantity of acid :

$20 - 2 = 18 \: litre$

We have to find how much water should be added so that percentage of water becomes 20%

Let, x litre should be added.

Then, according to the question :

$(2 + x) = (20 + x) \times \frac{20}{100} \\ \\ = > (2 + x) = \frac{(20 + x)}{5} \\ \\ = > 10 + 5x = 20 + x \\ \\ = > 4x = 10 \\ \\ = > x = 2.5$

So, 2.5 litre should be added to percentage of water becomes 20%