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
Volume = 40' × 60' × 0.5' = 1,200 cubic feet. Converting to cubic yards: 1,200 ÷ 27 = 44.4 cubic yards. Remember to convert inches to 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 6-inch thickness must be converted to 0.5 feet before multiplying. The final step divides by 27 since there are 27 cubic feet in one cubic yard (3×3×3=27).
Why the Other Options Are Wrong
Option B: 133.3 cubic yards
This answer appears to be the length times width (40×60÷6=400) with some incorrect manipulation of the thickness dimension, showing a fundamental misunderstanding of volume calculation.
Option D: 400 cubic yards
This answer likely results from an error in unit conversion, possibly converting thickness incorrectly or making a calculation mistake in the division process.
Memory Technique
Remember '27 to fly' - you need 27 cubic feet to make 1 cubic yard 'fly' off your calculation. Also remember 'ICF': Inches to feet, Calculate volume, Final conversion to yards.
Reference Hint
Look up concrete volume calculations and unit conversions in the construction materials chapter, specifically the section on concrete quantity estimation.
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