Question

When 1 litre of water was added to a mixture of acid and water, the new mixture contains 20% acid When 1 litre of acid is added to the new mixture, then the resulting mixture contains 33.33% acid. What was the percentage of acid in the original mixture?

• A. 25%
• B. 20%
• C. 33.33%
• D. 27.5%
• E. None of the above

Answer 1

The correct option is A 25%

After adding 1 L water, acid to water ratio is = 1: 4
If there is 5x litres of the solution, then x litres of acid and 4x litres of water.
Now, after adding 1 L acid, new ratio is $=1:2=x+1:4x\Rightarrow x+1=2\Rightarrow x=1$ litre
Before adding water, the ratio would have been = x: 4x-1 = 1: 3
Percentage of acid $=\frac{1}{4}\times 100=25\%$