What will come in place of the question mark (?) in the following equation, if ‘+’ and ‘–’ are interchanged and ‘×’ and ‘÷’ are interchanged? 1604 × 4 – 525 ÷ 5 + 73 = ?

Correct — A. Rewrite the whole line with the swaps in place, and only then compute.

Rule: + ↔ − and × ↔ ÷ ; BODMAS itself is unchanged.

1604 × 4 − 525 ÷ 5 + 73
becomes 1604 ÷ 4 + 525 × 5 − 73

1604 ÷ 4 = 401
525 × 5 = 2625

401 + 2625 = 3026
3026 − 73 = 2953 → option (a).

Why the others are wrong

• (b)
  2935 — 2935 is 2953 with the last two digits transposed. Every step of the swap and the arithmetic can be right and this still catches you at the moment you tick the option.
• (c)
  2539 — 2539 is another arrangement of the same four digits. No reading of 401 + 2625 − 73 produces it; the value is fixed at 2953.
• (d)
  2395 — 2395 is the fourth arrangement of 2, 9, 5 and 3. Reaching it would need a different quotient or product altogether, not a different reading of the swapped signs.

In a sign-interchange question you rewrite the expression once, in full, and only then compute. Doing the swap in your head while evaluating is where the mark goes.

After the swap, ordinary BODMAS applies — division and multiplication before addition and subtraction — because the question changes which symbols appear, never the order of operations.

Writing the rewritten line on the rough sheet costs a few seconds and removes the entire class of error.

Key facts

• After the interchange the expression reads 1604 ÷ 4 + 525 × 5 − 73.
• 1604 ÷ 4 = 401 and 525 × 5 = 2625.
• 401 + 2625 − 73 = 2953.

Common traps

• Applying BODMAS to the original expression and then trying to swap the answer.
• Exchanging + with × or − with ÷ — only like pairs are interchanged here.
• Computing 1604 × 4 out of habit because the printed symbol is ×.

No directly related past PYQ was found.