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 | ?
- (a) 9B
- (b) 3A
- (c) 3B ✓ UPSC's answer
- (d) 3C
Why the answer is (c)
• In each row, the third number is the difference between the second and first numbers: 10 - 7 = 3, 9 - 3 = 6, 13 - 10 = 3.
• In each row, the letters are A, B and C in some order, and the third letter is the one not present in the first two entries: B and A give C, C and B give A, A and C give B.
• Therefore the missing entry must have number 3 and letter B, i.e., 3B.
• Hence option (c) follows.
Why the other options are wrong
- (a) 9B
- 9B has the correct letter B but the wrong number because the row-wise number is 13 - 10 = 3, not 9.
- (b) 3A
- 3A has the correct number 3 but the wrong letter because row 3 already contains A and C, so the missing letter is B.
- (d) 3C
- 3C has the correct number 3 but the wrong letter because row 3 already contains C, so the missing letter is B.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.