Question

上周杂货店小盒面巾纸的价格是 $4$ 盒 $\$5$ 。本周促销价是 $5$ 盒 $\$4$ 。促销期间每盒价格下降的百分比最接近

At the grocery store last week, small boxes of facial tissue were priced at $4$ boxes for $\$5.$ This week they are on sale at $5$ boxes for $\$4.$ The percent decrease in the price per box during the sale was closest to

$30\%$

$35\%$

$40\%$

$45\%$

$65\%$

答案：B

知识点：百分数速率

难度评级：1280

解答：

原来每盒价格为 $\$ 5 \div 4 = \$ 1.25.$

现在每盒价格为 $\$ 4 \div 5 = \$ .8.$

下降百分比为 $\dfrac{1.25 - .8}{1.25} \cdot 100 \% = \dfrac{45}{125} \cdot 100 \%$ $= \dfrac{9}{25} \cdot 100 \% = 36 \%.$

所以正确答案是 B。

Originally, each box is worth $\$ 5 \div 4 = \$ 1.25.$

Now, each box is worth $\$ 4 \div 5 = \$ .8.$

The percent decrease is then $\dfrac{1.25 - .8}{1.25} \cdot 100 \% = \dfrac{45}{125} \cdot 100 \%$ $= \dfrac{9}{25} \cdot 100 \% = 36 \%.$

Thus, B is the correct answer.

1997 AMC 8 第 18 题

答案：B

难度评级：1280

解答：

其他年份的第 18 题