Question

Niki 通常让手机保持开机。如果手机开着但她实际上没有使用，电池能持续 $24$ 小时。如果她一直使用，电池只能持续 $3$ 小时。自上次充电以来，她的手机已经开机 $9$ 小时，其中她使用了 $60$ 分钟。如果她不再通话但保持手机开机，电池还能持续多少小时？

Niki usually leaves her cell phone on. If her cell phone is on but she is not actually using it, the battery will last for $24$ hours. If she is using it constantly, the battery will last for only $3$ hours. Since the last recharge, her phone has been on $9$ hours, and during that time she has used it for $60$ minutes. If she doesn’t talk any more but leaves the phone on, how many more hours will the battery last?

$7$

$8$

$11$

$14$

$15$

答案：B

知识点：速率分数

难度评级：1170

解答：

不使用时，手机每小时消耗 $\frac{1}{24}$ 的电量。使用时，每小时消耗 $\frac{1}{3}$ 的电量。

Niki 的手机开机 $9$ 小时，其中 $8$ 小时待机， $1$ 小时通话。

因此手机已消耗 $\frac{2}{3}$ 的电量。剩余 $\frac{1}{3}$ 电量在不使用时还能持续 $8$ 小时。

所以正确答案是 B。

When not in use, her cell phone uses up $\frac{1}{24}$ of its battery per hour. When it is in use, it uses up $\frac{1}{3}$ of its battery per hour.

Niki's phone has been on for $9$ hours, with $8$ of those hours being idle and $1$ hour being used to talk on the phone.

This means that the phone has used up $\frac{2}{3}$ of its battery. In order to drain the remaining $\frac{1}{3}$ of the battery, the phone can last for $8$ more hours without being used.

Thus, B is the correct answer.

2004 AMC 8 第 12 题

答案：B

难度评级：1170

解答：

其他年份的第 12 题