A concrete slab measures 40 feet by 60 feet and is 6 inches thick. How many cubic yards of concrete are needed?
Correct Answer
A) 44.4 cubic yards
Calculate: 40' × 60' × 0.5' = 1,200 cubic feet. Convert to cubic yards by dividing by 27: 1,200 ÷ 27 = 44.4 cubic yards. Always convert thickness to feet (6 inches = 0.5 feet) before calculating.
Why This Is the Correct Answer
Option A is correct because it follows the proper sequence of converting all measurements to the same unit (feet), calculating volume in cubic feet, then converting to cubic yards. The calculation converts 6 inches to 0.5 feet, multiplies 40' × 60' × 0.5' = 1,200 cubic feet, then divides by 27 to get 44.4 cubic yards. This is the standard method for concrete volume calculations in construction.
Why the Other Options Are Wrong
Option B: 53.3 cubic yards
This answer likely results from an error in unit conversion, possibly forgetting to convert the 6-inch thickness to feet or making an arithmetic mistake in the division by 27.
Option C: 66.7 cubic yards
This answer suggests the calculation may have used incorrect thickness conversion or failed to properly convert from cubic feet to cubic yards using the factor of 27.
Option D: 120 cubic yards
This answer appears to be the result in cubic feet (1,200) divided by 10 instead of 27, or possibly forgetting to convert from cubic feet to cubic yards entirely.
Memory Technique
Remember '27 to get away' - you must divide by 27 to get away from cubic feet and into cubic yards. Also, 'Inches to feet, divide by 12 to make it neat.'
Reference Hint
Look up concrete calculations and volume conversions in Chapter 3 (Materials and Methods) or the appendix conversion tables of your contractor reference manual.
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