UPSC Prelims 2026 · CSAT
Question 13: Basic Numeracy
A toy T jumps forward or backward. In each forward jump, it moves 5′ forward whereas in each backward jump, it moves 2′ backward. If in 31 jumps, T moves exactly 15′ forward, then what is the difference of the number of forward and backward jumps?
AnswerUPSC’s answer is (d).
Let F be the forward jumps and B the backward jumps. F + B = 31 and the net movement is 5F − 2B = 15. Put B = 31 − F: 5F − 62 + 2F = 15, so 7F = 77, giving F = 11 and B = 20. Check: 55 − 40 = 15. The difference between backward and forward jumps is 20 − 11 = 9.
Why each option is right or wrong
- (a) Wrong: with F = 11 and B = 20 the difference is 9, not 6.
- (b) Wrong: the difference is 9, not 7.
- (c) Wrong: the difference is 9, not 8.
- (d) Right: 20 − 11 = 9.
Only the provisional key (27 May 2026) was found; the final key replaces it when found.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2026, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.