r****o
发帖数: 27 | 1 题1
At how many minutes after noon do the hour hand and minute hand of an
analog clock first meet again? Express your answer to the nearet whole numer.
题2
Five people are arranged in a line. In how many ways can they be arranged
in a different order so that each person is standing beside at least one
person he or she originally stood beside?
希望大牛们在告诉我答案的同时也能简单的讲解一下这二个题的思路。谢谢。 | s*****V
发帖数: 21731 | 2 minute hand is faster than hour hand,so it can catch up the hour hand every
turn at some places. Assume h hour m minutes, they meet.
It is easy to write down the formula. Let us use primary school's method,
m hand runs at the speed 1 division per minute, the h hand runs at the speed
5/60 =1/12 divisions per minutes. To run 60 more divisions,
60/(1-1/12) = 720/11 | r****o
发帖数: 27 | 3 thanks Gave you a 包子
Anyone one know the other problem?
every
speed
【在 s*****V 的大作中提到】
: minute hand is faster than hour hand,so it can catch up the hour hand every
: turn at some places. Assume h hour m minutes, they meet.
: It is easy to write down the formula. Let us use primary school's method,
: m hand runs at the speed 1 division per minute, the h hand runs at the speed
: 5/60 =1/12 divisions per minutes. To run 60 more divisions,
: 60/(1-1/12) = 720/11
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