2019 CSAT, all questions
UPSC Prelims 2019 · CSAT
Question 14: Basic Numeracy
The number of parallelograms that can be formed from a set of four parallel lines intersecting another set of four parallel lines, is
a18
b24
c32
d36
AnswerUPSC’s answer is (d).
A parallelogram needs two lines from the first set of four parallel lines and two from the second set. Choosing 2 of 4 lines can be done in 4C2 = 6 ways for each set. Total = 6 × 6 = 36. Every choice of two lines from each set encloses exactly one parallelogram, and no other parallelogram can be formed from these eight lines.
Why each option is right or wrong
- (a) Wrong: undercounts; 6 choices from each set give 6 × 6.
- (b) Wrong: 24 undercounts the 36 combinations.
- (c) Wrong: 32 does not match 6 × 6.
- (d) Right: 6 × 6 = 36.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2019, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.