How many cubic yards of concrete are required for a 4-inch slab with a diameter of 15 feet?

• A. 3 cubic yards
• B. 2 1/2 cubic yards
• C. 1 1/2 cubic yards
• D. 4 cubic yards

Answer: (B)

Calculating the concrete volume for a slab relies on area times thickness, using the circle area formula for the footprint. The slab is circular with diameter 15 ft, so the radius is 7.5 ft. Area = πr^2 ≈ π × (7.5)^2 ≈ 176.7 ft². The thickness is 4 inches, which is 1/3 ft ≈ 0.333 ft. The volume in cubic feet is 176.7 × 0.333 ≈ 58.9 ft³. Since 1 cubic yard = 27 cubic feet, the volume is 58.9 / 27 ≈ 2.18 cubic yards. Practical rounding to the nearest listed option gives about 2.5 cubic yards. Therefore, the required amount is 2 1/2 cubic yards.