Introduction / Context:
This calculation tests careful handling of mixed numbers, nested brackets, and fraction operations. Accuracy requires converting mixed numbers to improper fractions, respecting the order of operations, and simplifying step by step.
Given Data / Assumptions:
- Expression: 5 - [ 3/4 + { 2 1/2 - ( 1/2 + 1/6 - 1/7 ) } ] / 2
- 2 1/2 is a mixed number, equal to 5/2
- Standard precedence: parentheses, then division/multiplication, then addition/subtraction
Concept / Approach:
Work from the innermost parentheses outward. Convert mixed numbers early. Keep everything as exact fractions to avoid rounding errors. Finally, subtract from 5 as an improper fraction with a common denominator.
Step-by-Step Solution:
Innermost: (1/2 + 1/6 - 1/7) = 1/2 + 1/6 = 2/3; 2/3 - 1/7 = 14/21 - 3/21 = 11/21Now: 2 1/2 - (result) = 5/2 - 11/21 = (105 - 22)/42 = 83/42Add 3/4: 3/4 + 83/42 = (63 + 166)/84 = 229/84Divide by 2: (229/84)/2 = 229/168Finally: 5 - 229/168 = (840 - 229)/168 = 611/168
Verification / Alternative check:
Approximate decimals: 611/168 ≈ 3.6369; evaluating the original numerically also gives ≈ 3.6369, confirming.
Why Other Options Are Wrong:
- 423/168, 583/168, 577/168: Each results from a common slip, such as reversing subtraction inside parentheses or forgetting to divide the bracketed sum by 2.
Common Pitfalls:
- Failing to convert 2 1/2 to 5/2 at the start.
- Not maintaining common denominators when adding/subtracting fractions.
Final Answer:
611/168
Discussion & Comments