When a runner was crossing the 12 km mark, she was informed that she had completed only 80% of the race. How many kilometres was the runner supposed to run in this event ?

(a) 14
(b) 15 ✓ UPSC's answer
(c) 16
(d) 16·5

Why the answer is (b)

• The problem states that the runner has covered 12 km, which represents 80% of the total race distance.

• Let the total distance of the race be denoted by 'D' kilometres.

• According to the given information, 80% of D is equal to 12 km, which can be written as the equation: 0.80 * D = 12.

• To find D, divide 12 by 0.80: D = 12 / 0.80.

• Performing the division gives D = 15 km.

• Therefore, the total distance of the race is 15 km, which corresponds to option (b).

Why the other options are wrong

(a) 14: 14 km is incorrect because 80% of 14 km is 11.2 km, not 12 km.
(c) 16: 16 km is incorrect because 80% of 16 km is 12.8 km, not 12 km.
(d) 16·5: 16.5 km is incorrect because 80% of 16.5 km is 13.2 km, not 12 km.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2019, held on 2 June 2019. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.