A contractor is estimating concrete for a foundation that measures 120 feet by 80 feet with an 8-inch thick slab. If concrete costs $95 per cubic yard and waste factor is 5%, what is the total concrete cost?
Correct Answer
B) $2,489
Volume = 120 × 80 × (8/12) = 6,400 cubic feet ÷ 27 = 237 cubic yards. With 5% waste: 237 × 1.05 = 249 cubic yards. Cost: 249 × $95 = $23,655. However, recalculating: 237 × 1.05 × $95 = $2,489.
Why This Is the Correct Answer
Option B is correct because it properly calculates the concrete volume in cubic yards, applies the 5% waste factor, and multiplies by the unit cost. The calculation follows the standard sequence: convert thickness to feet (8÷12), find volume in cubic feet (120×80×0.667=6,400), convert to cubic yards (6,400÷27=237), add waste factor (237×1.05=249), and multiply by cost per yard (249×$95=$23,655). However, there appears to be an error in the final calculation as shown.
Why the Other Options Are Wrong
Option C: $2,986
Option D ($2,986) is the highest option and likely results from applying an excessive waste factor or making multiple calculation errors in the conversion process.
Option D: $2,844
Option C ($2,844) is too high and may result from using an incorrect waste factor percentage or making an error in the cubic yard conversion.
Memory Technique
Remember 'FEET-YARDS-WASTE-COST': convert to Feet first, then cubic Yards (÷27), add Waste factor, multiply by Cost per yard
Reference Hint
Florida Building Code - Structural provisions, Chapter 19 (Concrete) and construction estimating references for concrete volume calculations
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