If + = ×, − = +, × = ÷; then 6 + 3 − 2 × 1 = ?

Correct — A. Swap the signs first, then evaluate.

Rule: + means ×, − means +, × means ÷, then BODMAS.

Printed: 6 + 3 − 2 × 1
Substituted: 6 × 3 + 2 ÷ 1

Multiply: 6 × 3 = 18
Divide: 2 ÷ 1 = 2
Add: 18 + 2 = 20 → option (a).

Why the others are wrong

• (b)
  21 — 21 would need 18 + 2 + 1, adding the final 1 instead of dividing by it. The printed × becomes ÷, and 2 ÷ 1 is just 2.
• (c)
  19 — 19 would need 18 + 2 − 1, subtracting the final 1. The printed × becomes ÷, so the last term is 2 ÷ 1 = 2 and the total is 20.
• (d)
  24 — 24 cannot be reached: every bracketing of 6 × 3 + 2 ÷ 1 gives 20 or 30, and BODMAS gives 20.

A sign-substitution item tests two steps in order: rewrite the expression with the new meanings, then evaluate it under BODMAS (brackets, orders, division and multiplication, addition and subtraction).

Rewrite the whole line before calculating. Swapping one sign at a time invites a double swap, such as turning a freshly written + into × again.

Here the order happens not to matter: left to right, 6 × 3 = 18, 18 + 2 = 20, 20 ÷ 1 = 20.

Key facts

• Under this key, 6 + 3 − 2 × 1 reads 6 × 3 + 2 ÷ 1.
• 6 × 3 + 2 ÷ 1 = 18 + 2 = 20.
• Multiplication and division are worked before addition and subtraction.

Common traps

• Swapping signs one at a time and turning a new + into × a second time.
• Reading the key backwards, as if a printed × meant +.

No directly related past PYQ was found.