Question

Sri 车里的钟不准，并且以恒定速度走快。某天他开始购物时，车钟和他准确的手表都显示中午十二点整。购物结束时，他的手表显示十二点三十分，车钟显示十二点三十五分。当天晚些时候，Sri 弄丢了手表。他看车钟，显示七点整。实际时间是多少？

The clock in Sri's car, which is not accurate, gains time at a constant rate. One day as he begins shopping he notes that his car clock and his watch (which is accurate) both say 12:00 noon. When he is done shopping, his watch says 12:30 and his car clock says 12:35. Later that day, Sri loses his watch. He looks at his car clock and it says 7:00. What is the actual time?

$5:50$

$6:00$

$6:30$

$6:55$

$8:10$

答案：B

知识点：时钟比与比例

难度评级：1140

视频讲解：

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文字解答：

从 $12:00$ 中午开始，真实经过 $30$ 分钟时，车钟走快到经过了 $35$ 分钟。

因此车钟每走一分钟，真实时间经过 $\frac {30}{35} = \frac 67$ 分钟。从 $12:00$ 到 $7:00$ ，车钟走了 $7\cdot 60 = 420$ 分钟，所以真实时间经过了 $420 \cdot \frac67 = 360$ 分钟，也就是 $6$ 小时。从 $12:00$ 开始经过 $6$ 小时，实际时间是 $6:00$ 。

所以正确答案是 B。

Starting from $12:00$ noon, after $30$ minutes of time elapsed, the car clock went $35$ minutes ahead.

Therefore, for every minute the car clock goes ahead, $\frac {30}{35} = \frac 67$ minutes of actual time pass by. From the time $12:00$ to $7:00,$ the car clock goes ahead $7\cdot 60 = 420$ minutes, and therefore, $420 \cdot \frac67 = 360$ minutes, or $6$ hours, of actual time have passed by. If we start at $12:00$ and $6$ hours pass by, the time is $6:00 .$

Thus, B is the correct answer.

2018 AMC 8 第 12 题

答案：B

难度评级：1140

视频讲解：

文字解答：

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