Calculate the volume of concrete needed for a rectangular foundation wall that is 100 feet long, 8 inches thick, and 8 feet high.
Correct Answer
B) 19.8 cubic yards
Volume = 100 ft × 0.67 ft (8 inches) × 8 ft = 533.3 cubic feet. Converting to cubic yards: 533.3 ÷ 27 = 19.8 cubic yards.
Why This Is the Correct Answer
Option B is correct because it properly converts all measurements to the same units (feet), calculates the volume in cubic feet, and then converts to cubic yards. The calculation follows the standard formula: Volume = Length × Width × Height, where 8 inches is correctly converted to 0.67 feet (8÷12). The final step divides by 27 to convert cubic feet to cubic yards, yielding 19.8 cubic yards.
Why the Other Options Are Wrong
Option A: 18.5 cubic yards
This answer is too low, likely resulting from an error in unit conversion or calculation. It may have used an incorrect conversion factor or made an arithmetic mistake in the division.
Option C: 21.2 cubic yards
This answer is too high, possibly from using incorrect units or failing to properly convert inches to feet. It might result from using 8 inches as 0.8 feet instead of the correct 0.67 feet.
Option D: 23.7 cubic yards
This answer is significantly too high, likely from a major calculation error such as not converting inches to feet at all, or using an incorrect conversion factor for cubic feet to cubic yards.
Memory Technique
Remember '27 to fly' - there are 27 cubic feet in 1 cubic yard (3×3×3=27). Also remember '12 inches per foot' for conversions.
Reference Hint
Look up concrete volume calculations in Chapter 3 (Materials and Methods) or the concrete/masonry section of your contractor reference manual.
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