If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive numbers in the equation 60_15_3_20_4 = 20 :
- (a) SPRQ
- (b) QRPS ✓ UPSC's answer
- (c) QRSP
- (d) SPQR
Why the answer is (b)
• The substitution given is P = +, Q = –, R = ×, S = ÷, and the equation to satisfy is 60 _ 15 _ 3 _ 20 _ 4 = 20.
• Option (b) QRPS translates to 60 – 15 × 3 + 20 ÷ 4 = 20.
• Applying BODMAS, the multiplication and division are performed first: 15 × 3 = 45 and 20 ÷ 4 = 5.
• The expression then reduces to 60 – 45 + 5, which is evaluated left to right: 60 – 45 = 15, then 15 + 5 = 20.
• The result equals 20, confirming that QRPS is the correct sequence of operators.
Why the other options are wrong
- (a) SPRQ
- SPRQ gives 60 ÷ 15 + 3 × 20 – 4 = 4 + 60 – 4 = 60, which does not equal 20.
- (c) QRSP
- QRSP gives 60 – 15 × 3 ÷ 20 + 4 = 60 – 2.25 + 4 = 61.75, which does not equal 20.
- (d) SPQR
- SPQR gives 60 ÷ 15 + 3 – 20 × 4 = 4 + 3 – 80 = –73, which does not equal 20.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.