UPSC Prelims 2026 · CSAT
Question 49: Basic Numeracy
How many times does 5 appear in all two-digit positive integers?
AnswerUPSC’s answer is (b).
Count the digit 5 by place. In the units place, 15, 25, ..., 95 give 9 numbers. In the tens place, 50 to 59 give 10 numbers. The number 55 has two 5s, one counted in each group, so the digit appears 9 + 10 = 19 times.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
This follows UPSC’s provisional key; the final key could change it.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: 18 drops one occurrence, usually the second 5 in 55.
- (b) Right: 9 + 10 = 19.
- (c) Wrong: 20 overcounts; the single digit 5 is not a two-digit number.
- (d) Wrong: 21 overcounts.
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.