题干

为了“绿色出行”,减少雾霾,家住番禺在广州中心城区上班的王经理,上班出行由自驾车改为乘坐地铁出行,已知王经理家距上班地点21千米,他用地铁方式平均每小时出行的路程,比他用自驾车平均每小时行驶的路程的2倍还多5千米,他从家出发到达上班地点,地铁出行所用时间是自驾车方式所用时间的
3
7
.求王经理地铁出行方式上班的平均速度.
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答案(点此获取答案解析)

解:设自驾车平均每小时行驶的路程为xkm,则有:

21x×37=212x+5

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    Every day, a homeowner in Pennsylvania is reminded of a mistake he made 13 years ago. At around 8 in the evening, his peaceful house comes alive with the noise of an alarm clock he dropped into the wall over ten years ago. It's been stuck in the wall ever since.

    13 years ago, Jerry Lynn wanted to make a hole through his living room wall, so he could pass the television cable (电缆)through it. He didn't want to destroy any pipes in the wall, so he came up with a good idea to make sure that he was drilling(钻孔) in an empty place. He took his alarm clock, tied it to a string(线) and set it to go off in 10 minutes. Then he lowered it into the wall, and waited for it to ring. His goal was to drill a hole in a safe place near the place where the ringing was coming from, making sure that there was nothing to pass through there. It all went smoothly until the alarm clock fell into the wall.

The man didn't get back the alarm clock, but thought it would probably run out of battery(电池)in several months, so he wasn't too worried about it. But 13 years later, the alarm clock still rings every day.

    As you can imagine, Jerry and his wife have gotten used to the ringing living room wall, but it can still surprise  guests. So Jerry decides to pull down that wall, just to stop that boring thing, though after putting up with it for 13 years, he think it will be a pity. He says, “I've never herd of a clock battery lasting that long and my friends think it may be interesting to see how long it will keep ringing for.”