2024 CSAT, all questions
UPSC Prelims 2024 · CSAT
Question 45: Basic Numeracy
What is the number of fives used in numbering a 260-page book?
a55
b56
c57
d60
AnswerUPSC’s answer is (b).
Count the digit 5 in pages 1 to 260. Units place: 5, 15, 25 and so on up to 255, which is 26 pages. Tens place: 50 to 59, 150 to 159 and 250 to 259, which is 3 × 10 = 30. No page has 5 in the hundreds place (that starts at 500). Total = 26 + 30 = 56. Remember that 55, 155 and 255 hold two fives each, once under units and once under tens.
Why each option is right or wrong
- (a) Wrong. 55 counts page 255 only once; it holds two fives.
- (b) Right. Units place 26 + tens place 30 = 56.
- (c) Wrong. 57 overcounts by one.
- (d) Wrong. 60 overcounts; the count is 26 + 30 = 56.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2024, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.