Q. A bottle contains 20 litres of liquid A.
4 litres of liquid A is taken out of it d replaced by same quantity of liquid B. Again 4 litre 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?
(a) 4:1
(b) 5:1
(c) 16:9
(d) 17: 8
Correct Answer: (c) 16:9
Question from UPSC Prelims 2020 CSAT Paper
Explanation :
PROBLEM: Find the final ratio of liquids A and B after two replacements
STEP 1: After First Replacement
– Liquid A = 16 litres
– Liquid B = 4 litres
– Total = 20 litres
– Ratio of A to total = 16/20 = 4/5
STEP 2: Second Replacement
– 4 litres mixture removed
– Liquid A removed = 4 × 4/5 = 3.2 litres
– Liquid A remaining = 16 – 3.2 = 12.8 litres
– Liquid B = 20 – 12.8 = 7.2 litres
STEP 3: Final Ratio
12.8:7.2 simplifies to 16:9
ANSWER: The final ratio of liquid A to liquid B is 16:9
