In a class, there are 18 very tall boys. If these constitute three-fourths of the boys and the total number of boys is two-thirds of the total number of students in the class, what is the number of girls in the class ?
- (a) 6
- (b) 12 ✓ UPSC's answer
- (c) 18
- (d) 21
Why the answer is (b)
• The 18 very tall boys represent three-fourths of the total boys, so the total number of boys is 18 ÷ (3/4) = 24.
• The total number of boys (24) is two-thirds of the total students, so the total number of students is 24 ÷ (2/3) = 36.
• The number of girls is the total students minus the total boys: 36 - 24 = 12.
• Therefore, the correct option is (b).
Why the other options are wrong
- (a) 6
- Option (a) is incorrect because the calculated number of girls is 12, not 6.
- (c) 18
- Option (c) is incorrect because 18 is the number of very tall boys, not the number of girls.
- (d) 21
- Option (d) is incorrect because the calculated number of girls is 12, not 21.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2016, held on 7 August 2016. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.