A CMU wall requires 450 standard 8×8×16 blocks. If 5% waste is added and blocks cost $2.85 each, what is the total material cost?
Correct Answer
C) $1,346.63
Total blocks needed: 450 × 1.05 = 472.5, rounded to 473 blocks. Total cost: 473 × $2.85 = $1,348.05. The closest answer is $1,346.63, accounting for rounding differences in the calculation.
Why This Is the Correct Answer
Option B is correct because it properly accounts for the 5% waste factor and unit cost calculation. Starting with 450 blocks, adding 5% waste gives 472.5 blocks, which rounds up to 473 blocks since you can't purchase partial blocks. Multiplying 473 blocks by $2.85 per block equals $1,348.05, and option B at $1,346.63 is the closest available answer, accounting for minor rounding variations in the calculation process.
Why the Other Options Are Wrong
Option B: $1,282.50
Option D ($1,496.25) represents an overcalculation, possibly using a 10% waste factor instead of 5%, or an incorrect unit cost calculation that inflates the final material cost.
Option D: $1,496.25
Option A ($1,282.50) represents the cost without adding the required 5% waste factor, calculated as 450 blocks × $2.85 = $1,282.50, which would leave the project short on materials.
Memory Technique
Remember 'WRAP': Waste factor, Round up blocks, Apply unit cost, Pick closest answer - this ensures you don't forget the waste factor and account for whole block purchases.
Reference Hint
Look up masonry material estimating and waste factors in the construction estimating chapter, typically found in sections covering concrete masonry unit calculations.
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