Correct Answer - Option 4 : 20 litres
Given:
Total initial mixture = 80 litres
The percentage of petrol in the mixture is 25%
Calculation:
The quantity of petrol in initial mixture = 25/100 × 80 = 20 litres
The quantity of ethanol in initial mixture = 80 - 20 = 60 litres
The amount of ethanol added be x
According to the question;
⇒ 20/(60 + x) = 20/80
⇒ 80 = 60 + x
⇒ x = 20 litres
∴ The amount of ethanol added is 20 litres