If 7 ⊕ 9 ⊕ 10 = 8, 9 ⊕ 11 ⊕ 30 = 5, 11 ⊕ 17 ⊕ 21 = 13, what is the value of 23 ⊕ 4 ⊕ 15 ?
- (a) 6 ✓ UPSC's answer
- (b) 8
- (c) 13
- (d) 15
Why the answer is (a)
• Add the three numbers in each expression: 7+9+10=26, 9+11+30=50, 11+17+21=49.
• Add the digits of that sum: 2+6=8, 5+0=5, 4+9=13.
• Apply the same rule to 23+4+15=42.
• Add the digits: 4+2=6, so option (a) follows.
Why the other options are wrong
- (b) 8
- 8 is incorrect because the digit sum of 42 is 4+2=6, not 8.
- (c) 13
- 13 is incorrect because the digit sum of 42 is 4+2=6, not 13.
- (d) 15
- 15 is incorrect because the digit sum of 42 is 4+2=6, not 15.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2023, held on 28 May 2023. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.