What is the volume, in gallons, of a trapezoidal trough?

• A. 9,000 gal
• B. 11,500 gal
• C. 12,000 gal
• D. 15,000 gal

Answer: (B)

Volume is found by taking the cross-sectional area of the trapezoid and multiplying it by the trough’s length. For a trapezoid, the cross-section area is the average of the two parallel sides (top and bottom widths) multiplied by the depth (the distance between those sides): A = ((top + bottom) / 2) × depth. Then the volume in cubic feet is V = A × length. To express that volume in gallons, convert from cubic feet using 1 ft^3 = 7.4805 gallons. If you plug in the dimensions shown in the diagram, you arrive at 11,500 gallons. Remember to keep all dimensions in feet (convert from inches if needed) before you calculate and then apply the gallon conversion.