Select the number that will come in the place of the question mark(?), if ‘+’ and ‘ – ‘ are interchanged and ‘×’ and ‘÷’ are interchanged 11 ÷ 12 – 78 × 6 + 57 = ?

Correct — C. Rewrite the line with the symbols exchanged, then apply BODMAS.

Given: 11 ÷ 12 − 78 × 6 + 57

Apply the swaps — + becomes −, − becomes +, × becomes ÷, ÷ becomes ×:
11 × 12 + 78 ÷ 6 − 57

Multiply: 11 × 12 = 132
Divide: 78 ÷ 6 = 13
Then left to right: 132 + 13 = 145, and 145 − 57 = 88

That is option (c).

Why the others are wrong

• (a)
  74 — Option (a) is 14 short. The swapped line opens with 11 × 12 = 132, because the printed ÷ becomes ×, so the first term is a product of two two-digit numbers and not a fraction near 0.9.
• (b)
  83 — Option (b) is 5 short. The middle term after the swap is 78 ÷ 6 = 13 exactly, with no remainder, so there is nothing to round away.
• (d)
  95 — Option (d) is 7 over, which is what you get from subtracting 50 instead of 57, or from reading 78 ÷ 6 as 20. Both slips land on 95.

The instruction changes the symbols on the page and nothing else. Write the substituted line out in full before computing, because the two swaps interact and doing them in your head is where errors come from.

Here the printed ÷ becomes ×, so a term that looked like the fraction 11 ÷ 12 turns into the product 11 × 12 = 132. That single change is most of the answer.

After the rewrite, ordinary BODMAS applies — multiply and divide first, then add and subtract from left to right.

Key facts

• After the interchange, 11 ÷ 12 − 78 × 6 + 57 reads 11 × 12 + 78 ÷ 6 − 57.
• 11 × 12 = 132 and 78 ÷ 6 = 13.
• 132 + 13 − 57 = 88.

Common traps

• Computing the printed line before applying the swaps
• Swapping the multiplication pair and forgetting the addition pair
• Reading 78 ÷ 6 as 20 rather than 13

No directly related past PYQ was found.