UPSC Prelims 2020 · CSAT
Question 16: Basic Numeracy
Let A3BC and DE2F be four-digit numbers where each letter represents a different digit greater than 3. If the sum of the numbers is 15902, then what is the difference between the values of A and D?
AnswerUPSC’s answer is (c).
All six letters are different digits from 4 to 9. Add column by column. Units: C + F must end in 2, so C + F = 12 with carry 1. Tens: B + 2 + 1 must end in 0, so B = 7 with carry 1. Hundreds: 3 + E + 1 = 9, so E = 5. The digits left are 4, 6, 8, 9: C and F are 4 and 8, so A and D are 6 and 9 (sum 15). They differ by 3.
Why each option is right or wrong
- (a) A and D are 6 and 9, which differ by 3, not 1.
- (b) A and D differ by 3, not 2.
- (c) Right: A and D are 9 and 6, a difference of 3.
- (d) A and D differ by 3, not 4.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.