A contractor is estimating concrete for a foundation that measures 120 feet by 80 feet with a thickness of 8 inches. How many cubic yards of concrete are needed?
Correct Answer
C) 237 cubic yards
Calculate: 120 ft × 80 ft × (8/12) ft = 6,400 cubic feet. Convert to cubic yards: 6,400 ÷ 27 = 237 cubic yards.
Why This Is the Correct Answer
Option C is correct because it follows the proper sequence of converting all measurements to the same units, calculating volume in cubic feet, then converting to cubic yards. The calculation converts 8 inches to 2/3 feet (8÷12), multiplies the dimensions (120 × 80 × 2/3 = 6,400 cubic feet), then divides by 27 to get cubic yards (6,400÷27 = 237.04, rounded to 237). This systematic approach ensures accuracy in concrete quantity estimation.
Why the Other Options Are Wrong
Option A: 178 cubic yards
This answer is too low, likely resulting from an error in unit conversion or calculation sequence, possibly forgetting to convert inches to feet or using an incorrect conversion factor.
Option B: 213 cubic yards
This answer is close but still incorrect, suggesting a minor calculation error or rounding mistake in the conversion process.
Option D: 284 cubic yards
This answer is too high, possibly from multiplying by an incorrect conversion factor or failing to properly convert the thickness from inches to feet.
Memory Technique
Remember 'FEET FIRST, THEN 27' - always convert everything to feet first, calculate cubic feet, then divide by 27 for cubic yards. Think '3 cubed = 27' for the conversion factor.
Reference Hint
Florida Building Code Chapter 19 - Concrete, or construction estimating references covering concrete volume calculations and unit conversions
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