2019 CSAT, all questions
UPSC Prelims 2019 · CSAT
Question 35: Basic Numeracy
Seeta and Geeta go for a swim after a gap of every 2 days and every 3 days respectively. If on 1st January both of them went for a swim together, when will they go together next ?
a7th January
b8th January
c12th January
d13th January
AnswerUPSC’s answer is (d).
A gap of 2 days means Seeta swims every 3rd day (1, 4, 7, 10, 13). A gap of 3 days means Geeta swims every 4th day (1, 5, 9, 13). They next meet after the LCM of 3 and 4, which is 12 days: 1 + 12 = 13 January. The trap is using the gaps 2 and 3 directly as the cycle, which gives 7 January.
Why each option is right or wrong
- (a) Wrong: uses the gaps 2 and 3 as the cycle instead of 3 and 4.
- (b) Wrong: 8 January is in neither schedule.
- (c) Wrong: 12 January is in neither schedule.
- (d) Right: both swim on 13 January.
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.