Reasoning : Logical Reasoning & Analytical Ability

Q 26 / 325

UPSC CSE Prelims 2025

If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive numbers in the equation 60_15_3_20_4=20:

EXPLANATION

Correct Option (B)

Given the symbol mapping: P = +, Q = –, R = ×, S = ÷. The target equation is 60 _ 15 _ 3 _ 20 _ 4 = 20.

For option (B) QRPS, the operations are Q (–), R (×), P (+), S (÷). Substituting these into the equation yields:

60 – 15 × 3 + 20 ÷ 4

Following the order of operations (BODMAS/PEMDAS):

  • First, perform division: 20 ÷ 4 = 5. The expression becomes: 60 – 15 × 3 + 5
  • Next, perform multiplication: 15 × 3 = 45. The expression becomes: 60 – 45 + 5
  • Then, perform subtraction: 60 – 45 = 15. The expression becomes: 15 + 5
  • Finally, perform addition: 15 + 5 = 20

Since the calculated result is 20, option (B) correctly satisfies the given equation.

Incorrect Options:

The other options do not yield the target value of 20 when their respective operations are applied following the order of operations.

  • Option (A) SPRQ: Operations are S (÷), P (+), R (×), Q (–).

    60 ÷ 15 + 3 × 20 – 4

    = 4 + 3 × 20 – 4

    = 4 + 60 – 4

    = 64 – 4

    = 60 (Not equal to 20)

  • Option (C) QRSP: Operations are Q (–), R (×), S (÷), P (+).

    60 – 15 × 3 ÷ 20 + 4

    = 60 – 45 ÷ 20 + 4

    = 60 – 2.25 + 4

    = 57.75 + 4

    = 61.75 (Not equal to 20)

  • Option (D) SPQR: Operations are S (÷), P (+), Q (–), R (×).

    60 ÷ 15 + 3 – 20 × 4

    = 4 + 3 – 20 × 4

    = 4 + 3 – 80

    = 7 – 80

    = -73 (Not equal to 20)

Explanation figure for the question: If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive nu… Explanation figure for the question: If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive nu… Explanation figure for the question: If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive nu… Explanation figure for the question: If P = +, Q = –, R = ×, S = ÷, then insert the proper notations between the successive nu…