2016 CSAT, all questions
UPSC Prelims 2016 · CSAT
Question 31: Basic Numeracy
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 ?
a6
b12
c18
d21
AnswerUPSC’s answer is (b).
Very tall boys are 3/4 of all boys, so boys = 18 x 4/3 = 24. Boys are 2/3 of the class, so students = 24 x 3/2 = 36. Girls = 36 - 24 = 12. Remember: work up the chain of fractions from the known number, then subtract.
Why each option is right or wrong
- (a) Gives 30 students; 24 boys would not be two-thirds.
- (b) Right: 24 boys plus 12 girls make 36, and boys are two-thirds.
- (c) Gives 42 students; 24 boys are not two-thirds.
- (d) Gives 45 students; 24 boys are not two-thirds.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2016, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.