从答案入手，凑数。答案的三个数都比较大，说明“主力军”是1分的，那么
90*1分+1*10分=100分，于是91是可能的
80*1分+1*20分=100分，但是没有20分的硬币，所以81不可能
75*1分+1*25分=100分，于是76也是可能的
KEY：91 and 76 If we can randomly imagine what is the value of coins in the box,can we reason there are 81 pennies in the box? If we can, answer 81 might be true too. 红绿灯问题。说路口的红绿灯在绿黄红三色间循环。灯亮的时间: Green: 40 seconds Yellow: 5 seconds Red: 45 seconds 问在一个5 minutes的时间段里红灯最多可以亮多少秒。 5 minutes = 300 seconds 把绿和黄看做一个整体A也是40+5=45秒，那么变成红和A的循环。因为300除不尽45，所以如果让红灯先亮，就可以把“余数”时间给红灯。300/(45+40+5)，商为3，余数为30，那么红灯最多亮3*45+30=165 KEY：165 The remainder may be 3, so ,the red light lasts 138 seconds, right? The remainder may be 3, so ,the red light lasts 138 seconds, right?
If we can randomly imagine what is the value of coins in the box,can we reason there are 81 pennies in the box?
If we can, answer 81 might be true too.
红绿灯问题。说路口的红绿灯在绿黄红三色间循环。灯亮的时间:
Green: 40 seconds
Yellow: 5 seconds
Red: 45 seconds
问在一个5 minutes的时间段里红灯最多可以亮多少秒。
5 minutes = 300 seconds
把绿和黄看做一个整体A也是40+5=45秒，那么变成红和A的循环。因为300除不尽45，所以如果让红灯先亮，就可以把“余数”时间给红灯。300/(45+40+5)，商为3，余数为30，那么红灯最多亮3*45+30=165
KEY：165 The remainder may be 3, so ,the red light lasts 138 seconds, right?
The remainder may be 3, so ,the red light lasts 138 seconds, right?
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