AMC8 1990

AMC8 1990 · Q17

AMC8 1990 · Q17. It mainly tests Fractions, Unit conversion.

A straight concrete sidewalk is to be 3 feet wide, 60 feet long and 3 inches thick. How many cubic yards of concrete must a contractor order for the sidewalk if concrete must be ordered in a whole number of cubic yards?

一条直线混凝土人行道宽 3 英尺，长 60 英尺，厚 3 英寸。承包商需要订购多少立方码混凝土，如果混凝土必须以整数量的立方码订购？

(A) 2 2

(B) 5 5

(D) 20 20

(E) more than 20 超过 20

Answer

Correct choice: (A)

正确答案：（A）

Solution

Answer (A): The number of cubic feet is $3 \times 60 \times \frac{1}{4} = 45$. Since there are 27 cubic feet in 1 cubic yard, there are $\frac{45}{27} = 1\tfrac{2}{3}$ cubic yards of concrete required. Thus 2 cubic yards must be ordered.

答案（A）：立方英尺的数量为 $3 \times 60 \times \frac{1}{4} = 45$。由于 1 立方码等于 27 立方英尺，因此需要的混凝土体积为 $\frac{45}{27} = 1\tfrac{2}{3}$ 立方码。因此必须订购 2 立方码的混凝土。

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