Interchange one pair of signs to make the equation true: 5 × 15 ÷ 7 − 20 + 4 = 77

Introduction / Context:We must swap one pair of operators globally so that the evaluated left side equals 77.

Given Data / Assumptions:

• Expression: 5 × 15 ÷ 7 − 20 + 4.
• Target value: 77.

Concept / Approach:Check each candidate swap; recompute with standard precedence.

Step-by-Step Solution:Swap “+” and “÷” (Option C): the expression becomes 5 × 15 + 7 − 20 ÷ 4.Compute: 5 × 15 = 75; then +7 → 82; 20 ÷ 4 = 5; finally 82 − 5 = 77 ✔.

Verification / Alternative check:Other swaps (e.g., ×↔÷ or −↔+) do not reach 77.

Why Other Options Are Wrong:They give values like ~26.7, −72.9, etc., not 77.

Common Pitfalls:Accidentally swapping only a single occurrence instead of all.

Final Answer:+ and ÷.