2021 CSAT, all questions
UPSC Prelims 2021 · CSAT
Question 27: Logical Reasoning and Mental Ability
Following is a matrix of certain entries. The entries follow a certain trend row-wise. Choose the missing entry (?) accordingly.
| 7B | 10A | 3C |
| 3C | 9B | 6A |
| 10A | 13C | ? |
a9B
b3A
c3B
d3C
AnswerUPSC’s answer is (c).
Look along each row. The letters in each row are A, B and C in some order, so the missing letter in row 3 is B. For the numbers, the third entry equals the second minus the first: 10 − 7 = 3 and 9 − 3 = 6, so row 3 gives 13 − 10 = 3. The missing entry is 3B. Remember: when a puzzle mixes numbers and letters, treat them as two separate patterns and solve each on its own.
Why each option is right or wrong
- (a) 9B has the right letter but the number should be 13 − 10 = 3.
- (b) 3A has the right number but A is already used in the row.
- (c) Right: number 13 − 10 = 3, and B is the letter missing from the row.
- (d) 3C repeats C, which is already in the row.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.