Question

Maria 以每 $4$ 张 $5 的价格买入电脑磁盘，并以每 $3$ 张 $5 的价格卖出。她必须卖出多少张电脑磁盘，才能获利 $100？

Maria buys computer disks at a price of $4$ for $5 and sells them at a price of $3$ for $5. How many computer disks must she sell in order to make a profit of $100?

$100$

$120$

$200$

$240$

$1200$

答案：D

知识点：比与比例

难度评级：1110

解答：

按打计算磁盘，因为 $12$ 同时是 $4$ 和 $3$ 的倍数。一打磁盘买入需 $3 \times \$5 = \$15$ ，卖出可得 $4 \times \$5 = \$20$ ，每打利润为 $5。

要获利 $100，她需要 $\dfrac{100}{5} = 20$ 打，也就是 $20 \times 12 = 240$ 张磁盘。

所以正确答案是 D。

Consider disks in dozens, since $12$ is a multiple of both $4$ and $3.$ A dozen disks costs $3 \times \$5 = \$15$ to buy and sells for $4 \times \$5 = \$20,$ for a profit of $5 per dozen.

To make $100 profit she needs $\dfrac{100}{5} = 20$ dozen, which is $20 \times 12 = 240$ disks.

Thus, the correct answer is D .

1988 AMC 8 第 23 题

答案：D

难度评级：1110

解答：

其他年份的第 23 题