UPSC Prelims 2017 · CSAT

Question 80: Basic Numeracy

What is the total number of digits printed, if a book containing 150 pages is to be numbered from 1 to 150 ?

a262

b342

c360

d450

AnswerUPSC’s answer is (b).

Count digits by page range. Pages 1 to 9: 9 pages with 1 digit each = 9. Pages 10 to 99: 90 pages with 2 digits = 180. Pages 100 to 150: 51 pages with 3 digits = 153. Total: 9 + 180 + 153 = 342. Remember the range sizes: 9, 90 and 900 numbers for 1, 2 and 3 digits.

Why each option is right or wrong

(a) 262 does not match the range-by-range count.
(b) Correct: 9 + 180 + 153 = 342.
(c) 360 does not match the range-by-range count.
(d) 450 would be 150 x 3, treating every page as three-digit.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2017, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.