What will come in place of the question mark (?) in the following equation, if ‘+’ and ‘÷’ are interchanged and ‘×’ and ‘−’ are interchanged? 20 + 4 ÷ 2 × 3 − 6 = ?

Correct — A. Swap the signs on the page first, then compute.

Rule: '+' becomes '÷', '÷' becomes '+', '×' becomes '−' and '−' becomes '×'.

20 + 4 ÷ 2 × 3 − 6 rewrites as 20 ÷ 4 + 2 − 3 × 6.
20 ÷ 4 = 5
3 × 6 = 18
5 + 2 − 18 = −11 → option (a)

Why the others are wrong

• (b)
  −7 — −7 needs the closing product to be 14, since 5 + 2 − 14 = −7. The swapped line ends in 3 × 6 = 18, so check that multiplication before you doubt the swap.
• (c)
  2 — 2 is positive, and it cannot be. After the swap the line ends with − 3 × 6 = −18 against only 5 + 2 = 7 in front of it, so the result has to be negative.
• (d)
  −9 — −9 needs the final product to come out 16 rather than 18. The substitution was applied correctly here; the multiplication was not.

Symbol-substitution items test two habits at once: rewriting the line before computing, and then obeying BODMAS on the rewritten line.

The swap only relabels the printed signs. It does not change the order of operations, so division and multiplication are still settled before addition and subtraction.

Working the rewritten line left to right gives 24 here instead of −11. That single habit is the whole gap between a right and a wrong answer.

Key facts

• After the interchange the line reads 20 ÷ 4 + 2 − 3 × 6.
• BODMAS survives the swap: × and ÷ are settled before + and −.
• 5 + 2 − 18 = −11.

Common traps

• Computing the printed line first and trying to adjust the answer afterwards.
• Applying a swap in one direction only, so '+' becomes '÷' but '÷' stays put.
• Running the rewritten line left to right, which gives 24 here.

No directly related past PYQ was found.