UPSC Prelims 2014 · CSAT
Question 42: Logical Reasoning and Mental Ability
Consider the table given below in which the numbers bear certain relationship among themselves along the rows :
| 29 | 13 | 18 |
| 33 | X | 19 |
| 30 | 27 | 3 |
Which one of the following numbers is the missing number indicated above by X ?
AnswerUPSC’s answer is (b) or (d).
Look for a rule along the rows. The numbers in each row add to the same total: 29 + 13 + 18 = 60 and 30 + 27 + 3 = 60. In the middle row, 33 + X + 19 must also be 60, so X = 8. The key accepts 15 as well as 8, but with the numbers as printed here the row-sum rule gives only 8.
Why each option is right or wrong
- (a) 19 does not make the row total 60.
- (b) Accepted by the key, though the row-sum rule with the numbers as printed gives 8 rather than 15.
- (c) 14 does not make the row total 60.
- (d) Fits the row-sum rule: 33 + 8 + 19 = 60.
Worth knowing: UPSC's key accepts both (b) and (d); with the numbers as printed, the row-sum rule gives 8 only.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2014, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.