Question

Raj preparing an alcohol solution that contains 20% alcohol. But after the preparation, he found that the alcohol content was only 18%. If the volume of the prepared solution was 100 Litres, how much more alcohol is needed to make it 20% solution?
1. 2
2. 2.5
3. 4
4. 5

Answer 1

Correct Answer - Option 2 : 2.5

Calculation:

The volume of alcohol in the mixture = 18% of 100 litres = 18 Litres

Let P is the alcohol needed to add into the solution,

Total volume of the solution = 100 + P

⇒ 20% of (100 + P) litres = 18 + P

⇒ (100 + P) × (20/100) = 18 + P

⇒ 20 + 0.2P = 18 + P

⇒ 0.8P = 2

⇒ P = 2.5 Litre

If a mixture of Q1 quantity C1% content is mixing with Q2 quantity C2% mixture, and the concentration of the new mixture is Cnew% , then the following equation can be used:

C1% of Q1 + C2% of Q2 = Cnew% of (Q1 + Q2)

⇒ C1Q1 + C2Q2 = Cnew(Q1 + Q2)