2023 CSAT, all questions
UPSC Prelims 2023 · CSAT
Question 7: Basic Numeracy
What is the remainder when 85 × 87 × 89 × 91 × 95 × 96 is divided by 100 ?
a0
b1
c2
d4
AnswerUPSC’s answer is (a).
Look for factors that build 100 = 4 x 25. 85 = 5 x 17 and 95 = 5 x 19 each carry one 5, giving 25. 96 = 2^5 x 3 supplies the factors of 2 needed for 4. So the product is a multiple of 100 and the remainder is 0. No need to multiply everything out: when the product contains both 25 and 4 as factors, it is divisible by 100.
Why each option is right or wrong
- (a) Right: the product contains 25 and 4, so 100 divides it.
- (b) Wrong: the remainder is 0, not 1.
- (c) Wrong: the remainder is 0, not 2.
- (d) Wrong: the remainder is 0, not 4.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2023, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.