Question

Difficulty: MediumRectangular Area Applications

A contractor is applying a specialized primer to a rectangular warehouse wall that is 60 feet60\text{ feet} long and 18 feet18\text{ feet} high. The wall contains a rectangular loading bay door measuring 30 feet30\text{ feet} long and 12 feet12\text{ feet} high, which will not receive the primer. If the primer material costs $15\$15 per square yard, what is the total cost, in dollars, of the primer needed for the wall?

Answer: 1200 $

Answer

1200
The total gross area of the wall is 60×18=1080 square feet60 \times 18 = 1080\text{ square feet}. The area of the unpainted loading door is 30×12=360 square feet30 \times 12 = 360\text{ square feet}. Subtracting the door's area yields a net area of 720 square feet720\text{ square feet} to be primed. Because 1 square yard1\text{ square yard} equals 9 square feet9\text{ square feet}, the net area in square yards is 720÷9=80 square yards720 \div 9 = 80\text{ square yards}. Finally, multiplying the 80 square yards80\text{ square yards} by the $15\$15 cost per square yard gives a total cost of $1200\$1200.

Step-by-Step Solution

1
Calculate the gross area of the warehouse wall.
1080 sq ft1080\text{ sq ft}
Multiply the length (60 feet60\text{ feet}) by the height (18 feet18\text{ feet}) to find the total rectangular area before accounting for the door.
2
Calculate the area of the loading bay door.
360 sq ft360\text{ sq ft}
Multiply the door's length (30 feet30\text{ feet}) by its height (12 feet12\text{ feet}) to determine the area that will not be painted.
3
Find the net area to be primed.
720 sq ft720\text{ sq ft}
Subtract the area of the door from the gross wall area (1080−3601080 - 360) to find the exact surface area requiring primer.
4
Convert the net square footage into square yards.
80 sq yd80\text{ sq yd}
Since the cost is given per square yard, and there are 9 square feet9\text{ square feet} in 1 square yard1\text{ square yard} (3 ft×3 ft3\text{ ft} \times 3\text{ ft}), divide the net area by 9 (720÷9720 \div 9).
5
Calculate the total cost of the primer.
$1200\$1200
Multiply the required area in square yards (8080) by the cost per square yard ($15\$15).

Key Concept

Calculating net rectangular area via subtractive cutouts and applying square unit conversions.
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