In the shortcut method for a 4-inch slab, the volume in cubic yards is found by dividing the circle area by which number?

• A. 27
• B. 81
• C. 9
• D. 63

Answer: (B)

When using the shortcut method for a circular slab, you’re converting a circle’s area in square feet into a volume in cubic yards. Start by taking the circle’s area in square feet, then multiply by the thickness in feet. For a 4-inch slab, thickness is 4 inches = 1/3 foot. So volume in cubic feet is the area times 1/3. To convert cubic feet to cubic yards, divide by 27 (since 1 cubic yard = 27 cubic feet). Put together, you multiply by 1/3 and then divide by 27, which is the same as dividing by 81. Therefore, the volume in cubic yards equals the circle area (in square feet) divided by 81.