Question

Joe is finding the length of a rectangular prism. The volume of the prism is 204 ft3. The width is 3.5 ft, and the height is 5 ft. His work is shown below.

V = l w h. 204 = 3.5 (5) l. 204 = 8.5 l. StartFraction 204 Over 8.5 EndFraction = StartFraction 8.5 Over 8.5 EndFraction l. 24 = l.

What error did Joe make?
He incorrectly substituted into the volume formula.
He added 3.5 and 5 when he should have multiplied them.
He incorrectly divided 204 by 8.5.
He did not make a mistake in finding the length of the prism.

Answer 1

He added 3.5 and 5 when he should have multiplied them.

Explanation:

Volume = length × width × height

204 = 3.5 × 5 × length

204 = 17.5 × lenth

length = 204/17.5

length = 11.65714286

Answer 2

B. He added 3.5 and 5 when he should have multiplied them.

Explanation:

Let's observe Joe's steps:

- V = lwh

- 204 = 3.5 * (5) * l

Here, * means to multiply, so we're supposed to multiply 3.5 to 5, which would give you the answer 17.5. Unfortunately, look what Joe got: he obtained the value of 8.5, and if we observe, 3.5 + 5 = 8.5.

That's how we know that Joe added instead of multiplied, as he should have done. Thus, the answer is B.