How many cubic yards of concrete are needed for a 4-inch-thick circular slab with a circumference of 25 feet?

How many cubic yards of concrete are needed for a 4-inch-thick circular slab with a circumference of 25 feet?

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

Answer: (A)

To find the needed volume, use volume = area × thickness. First convert the circumference to radius: r = C/(2π) = 25/(2π) ≈ 3.98 ft. Then the slab area is πr^2 ≈ π(3.98)^2 ≈ 49.8 ft^2. The thickness is 4 inches, which is 1/3 ft, so the volume is 49.8 × 1/3 ≈ 16.6 ft^3. Convert to cubic yards by dividing by 27: 16.6/27 ≈ 0.615 yd^3. The closest option is 0.75 cubic yards, i.e., 3/4 cu yd.

To find the needed volume, use volume = area × thickness. First convert the circumference to radius: r = C/(2π) = 25/(2π) ≈ 3.98 ft. Then the slab area is πr^2 ≈ π(3.98)^2 ≈ 49.8 ft^2. The thickness is 4 inches, which is 1/3 ft, so the volume is 49.8 × 1/3 ≈ 16.6 ft^3. Convert to cubic yards by dividing by 27: 16.6/27 ≈ 0.615 yd^3. The closest option is 0.75 cubic yards, i.e., 3/4 cu yd.