A concrete slab spans 15 feet by 12 feet with a thickness of 4 inches. It includes a central cutout of 3 feet by 3 feet. How much concrete is required in cubic yards?

• A. 2 1/2 cu yds
• B. 2 cu yds
• C. 2 1/4 cu yds
• D. 3 cu yds

Answer: (C)

The main idea is to find the net volume of concrete by calculating the solid slab and then subtracting the hollow cutout, using consistent units and converting to cubic yards at the end.

First, the slab area is 15 ft × 12 ft = 180 ft². The thickness is 4 inches, which is 1/3 ft, so the solid-volume would be 180 × 1/3 = 60 ft³. The central cutout is 3 ft × 3 ft = 9 ft², and with the same thickness its volume is 9 × 1/3 = 3 ft³. Subtracting the cutout gives a net volume of 60 − 3 = 57 ft³.

Convert to cubic yards: 57 ft³ ÷ 27 = 2.111… yd³. In practice, you’d round to the nearest quarter-yard for estimating, which gives about 2.25 yd³, i.e., 2 1/4 cubic yards.