Two equal glasses of same type are respectively 1/3 and 1/4 full of milk. They are then filled up with water and the contents are mixed in a pot. What is the ratio of milk and water in the pot ?

(a) 7 : 17 ✓ UPSC's answer
(b) 1 : 3
(c) 9 : 21
(d) 11 : 23

Why the answer is (a)

• Let the capacity of each glass be 12 units (LCM of 3 and 4) to simplify calculations.

• The first glass contains 1/3 of 12 = 4 units of milk and is filled with 8 units of water.

• The second glass contains 1/4 of 12 = 3 units of milk and is filled with 9 units of water.

• Total milk in the pot is 4 + 3 = 7 units.

• Total water in the pot is 8 + 9 = 17 units.

• Therefore, the ratio of milk to water is 7 : 17.

Why the other options are wrong

(b) 1 : 3: Option (b) 1:3 is incorrect because the total milk is 7 units and total water is 17 units, not 1 and 3.
(c) 9 : 21: Option (c) 9:21 is incorrect because the calculated milk quantity is 7 units, not 9 units.
(d) 11 : 23: 11 : 23 would need 11 parts of milk in 34; the pot actually has 7 parts milk to 17 parts water.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.