2024 CSAT, all questions
UPSC Prelims 2024 · CSAT
Question 75: Logical Reasoning and Mental Ability
If a + b means a − b; a − b means a × b; a × b means a ÷ b; a ÷ b means a + b, then what is the value of 10 + 30 − 100 × 50 ÷ 25 ? (Operations are to be replaced simultaneously)
a15
b0
c−15
d−25
AnswerUPSC’s answer is (d).
Replace the symbols all at once: + becomes −, − becomes ×, × becomes ÷ and ÷ becomes +. The expression 10 + 30 − 100 × 50 ÷ 25 turns into 10 − 30 × 100 ÷ 50 + 25. Now apply BODMAS: 30 × 100 ÷ 50 = 60, so 10 − 60 + 25 = −25. Remember to substitute every symbol first, before calculating anything.
Why each option is right or wrong
- (a) Wrong. 15 does not equal 10 − 60 + 25.
- (b) Wrong. 0 does not equal 10 − 60 + 25.
- (c) Wrong. −15 does not equal 10 − 60 + 25.
- (d) Right. 10 − 60 + 25 = −25.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2024, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.