Geometry and Trigonometry practice question

Answer: B. 60

Volume of a rectangular prism is V = lwh = 5 · 4 · 3 = 60 cubic inches. (A) is the sum of the three dimensions, 5 + 4 + 3 = 12, the error of adding instead of multiplying. (C) is the surface area, 2(5·4) + 2(5·3) + 2(4·3) = 40 + 30 + 24 = 94, the error of using the surface-area formula instead of the volume formula. (D) is 2lwh = 120, the error of doubling the product (as one does for pairs of faces in surface area) when computing volume.

Why the other answers are wrong

A. 12

You added the three dimensions (5 + 4 + 3) instead of multiplying them. Volume is lwh = 5 · 4 · 3 = 60.

C. 94

That's the surface area, 2(20) + 2(15) + 2(12) = 94. The question asks for volume, which is just lwh = 60.

D. 120

You doubled the product, 2 · 5 · 4 · 3 = 120. Doubling belongs to surface area (pairs of faces); volume is simply lwh = 60.

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