A bottle contains 20 litres of liquid Q. 4 litres of liquid A is taken out

A bottle contains 20 litres of liquid Q. 4 litres of liquid A is taken out of its and replace by same quantity of liquid B. Again 4 litres of the mixture is taken out and replaced by same quantity of liquid B. What is the ratio of quantity of liquid A to that of liquid B in the final mixture?

  1. 4 : 1
  2. 5 : 1
  3. 16 : 9
  4. 17 : 8

Answer: C

Explanation

Method I

So, ratio of A and B in the final mixture = 64/5 : 36/5 = 16 : 9

Method II:

Just focus on liquid A. Out of initial 20 liters, 4 liters is taken out, i.e. a decrease of 20%.

This process is repeated again, i.e. again a decrease of 20%. So, this is a case of successive percentage change.

Net percentage change = x + y + (xy/100) = -20 - 20 + 4 = 36%

So, if initially liquid A was 100 liters, now after 36% reduction, only 64 liters is left. The rest 36 liters is liquid B.

So, ratio of A and B in the final mixture = 64 : 36 = 16 : 9

  • Exam Year: 2020