If '+' means '−', '−' means '×', '÷' means '+', and '×' means '÷', then what will be the value of the following expression?

Question

If '+' means '−', '−' means '×', '÷' means '+', and '×' means '÷', then what will be the value of the following expression?

21 × 7 ÷ 4 − 5 + 3 = ?

Choose the correct answer:

1. A. 56
2. B. 20 (Correct answer)
3. C. 32
4. D. 144

Correct Answer

Option B — 20

Detailed Solution & Explanation

The correct answer is 20.

Key Points

• Substitute each symbol by its stated meaning: '×' becomes ÷, '÷' becomes +, '−' becomes ×, '+' becomes −.
• The expression 21 × 7 ÷ 4 − 5 + 3 therefore becomes 21 ÷ 7 + 4 × 5 − 3.
• Apply BODMAS to the substituted expression: 21 ÷ 7 = 3, and 4 × 5 = 20.
• So the value is 3 + 20 − 3 = 20.

Additional Information

• Substitute first, then apply the order of operations — reversing these two steps is the usual source of error.
• In such items the original expression is deliberately arranged so that reading it at face value (21 × 7 = 147) leads nowhere near an option.

*Ministry of Papers worked solution. The Commission has not yet published the official key for this paper; this answer will be reconciled with it on release.*