2019 CSAT, all questions
UPSC Prelims 2019 · CSAT
Question 9: Basic Numeracy
The number of times the digit 5 will appear while writing the integers from 1 to 1000 is
a269
b271
c300
d302
AnswerUPSC’s answer is (c).
Count each place value separately for 000 to 999. The digit 5 appears in the units place in 100 numbers (5, 15, 25 and so on), in the tens place in 100 numbers (50 to 59, 150 to 159 and so on), and in the hundreds place in 100 numbers (500 to 599). Total = 100 + 100 + 100 = 300. The number 1000 has no 5. Do not confuse this with 271, the count of numbers containing at least one 5.
Why each option is right or wrong
- (a) Wrong: does not match 100 appearances in each of three places.
- (b) Wrong: 271 is how many numbers contain a 5, not how many times 5 is written.
- (c) Right: 100 per place, three places.
- (d) Wrong: 302 overcounts; 1000 contains no 5.
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.