2013 CSAT, all questions
UPSC Prelims 2013 · CSAT
Question 48: Logical Reasoning and Mental Ability
Consider the following matrix :
| 3 | 370 | 7 |
| 2 | 224 | 6 |
| 1 | 730 | X |
What is the number at ‘X’ in the above matrix ?
a5
b8
c9
d11
AnswerUPSC’s answer is (c).
Test a rule on the complete rows. Row 1: 3 and 7 give 3^3 + 7^3 = 27 + 343 = 370. Row 2: 2 and 6 give 2^3 + 6^3 = 8 + 216 = 224. So the middle number is the sum of the cubes of the outer numbers. Row 3: 1^3 + X^3 = 730, so X^3 = 729 and X = 9.
Why each option is right or wrong
- (a) Wrong. 5 gives 1 + 125 = 126, not 730.
- (b) Wrong. 8 gives 1 + 512 = 513, not 730.
- (c) Right. 1 + 729 = 730.
- (d) Wrong. 11 gives 1 + 1331 = 1332, not 730.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.