Question

How many litres of water should be added to a 7.5 litre mixture of acid and water containing acid and water in the ratio of 1 : 2 such that the resultant mixture has 20% acid in it?

• A. 10
• B. 2.5
• C. 7.5
• D. 5

Answer 1

Answer:

D. 5

Solution:

Given :

A mixture of acid and water in ratio 1 :  2 

Volume of mixture is 7.5 litre 

Calculations :

According to the question

Amount of acid in the mixture $=(\frac{1}{3})\times{7.5} = 2.5$

 

Amount of water in the mixture $=(\frac{2}{3})\times{7.5} = 5$

 

Let the amount of water added be 'x' litres to make it 20% acid in mixture

Amount of water will be in new mixture will be 80% 

So, 

(Initial amount of water + Amount of water to be added)/(Initial amount of acid) $=\frac{80}{20}$

 

$\frac{(5 + x)}{2.5} = \frac{4}{1}$

 

⇒ x = 5 

∴ 5 litre water should be added to make new mixture having 20% acid