A bathroom floor requires 450 square feet of 12"×12" ceramic tile. If tiles come 20 per box and the contractor adds 10% waste, how many boxes are needed?
Correct Answer
B) 25 boxes
Each tile covers 1 sq ft, so 450 tiles needed. With 10% waste: 450 × 1.10 = 495 tiles. Divided by 20 tiles per box: 495 ÷ 20 = 24.75, rounded up to 25 boxes.
Why This Is the Correct Answer
The calculation correctly identifies that each 12"×12" tile covers exactly 1 square foot, requiring 450 tiles for the floor area. Adding 10% waste factor (450 × 1.10 = 495 tiles) accounts for cuts, breakage, and future repairs. Since tiles come 20 per box, dividing 495 by 20 gives 24.75 boxes, which must be rounded up to 25 complete boxes since partial boxes cannot be purchased.
Why the Other Options Are Wrong
Option A: 23 boxes
This answer of 23 boxes fails to account for the 10% waste factor, only calculating the exact tile count (450 ÷ 20 = 22.5, rounded to 23), which would leave the contractor short of materials.
Option C: 27 boxes
This answer of 27 boxes overestimates the requirement, possibly calculating with a higher waste percentage (around 20%) or making an error in the division step.
Option D: 30 boxes
This answer of 30 boxes significantly overestimates the need, representing approximately a 33% waste factor, which is excessive for standard tile installation.
Memory Technique
Remember 'WAR': Waste factor first, Add to base quantity, Round UP to whole packages - you can't buy half a box!
Reference Hint
Florida Building Code Chapter 4 - Materials and Construction, or construction estimating references covering material takeoffs and waste factors
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