Difficulty: Hard
Correct Answer: − and +
Explanation:
Introduction / Context:
This question tests operator precedence and careful checking. You must swap exactly two operator symbols in the expression so that, after applying the standard order of operations, the left-hand side becomes 8.
Given Data / Assumptions:
Concept / Approach:
Try swapping candidate operator pairs and re-evaluate the left-hand side using the correct precedence rules. Because only one swap is allowed, we look for the unique pair that makes the value exactly 8.
Step-by-Step Solution:
1) Evaluate original to confirm it is wrong:
4 × 3 = 12 and 6 ÷ 2 = 3
LHS = 12 − 3 + 7 = 16 (not 8)
2) Swap the positions of − and +, giving:
4 × 3 + 6 ÷ 2 − 7
3) Apply precedence again:
4 × 3 = 12
6 ÷ 2 = 3
4) Now combine with + and −:
LHS = 12 + 3 − 7 = 8
5) This matches the required RHS (8), so the swap is correct.
Verification / Alternative check:
The corrected equation is:
4 × 3 + 6 ÷ 2 − 7 = 8
Since 12 + 3 − 7 = 8 exactly, the fix is valid without ambiguity.
Why Other Options Are Wrong:
• × and +: changes the structure but does not yield 8 with precedence.
• ÷ and ×: produces a different multiplication/division pattern, not 8.
• × and −, or − and ÷: similarly fail to produce 8 after precedence.
Common Pitfalls:
• Evaluating strictly left-to-right and ignoring precedence.
• Swapping operator meanings instead of swapping their positions.
Final Answer:
− and +
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