一道数学题的讨论

sxu0501 · 发表于 2016-11-21 13:50:49

各位大神们，
遇到一个数学题，完全蒙了。请问怎么解？
Traffic light A are green for 40 sec, and then turn yellow for 5 sec, before turing red for 45 sec.
Traffic light B are gree for 35 sec, and then turn yellow for 5 sec, before turing red for 35 sec.
Both of these two sets of traffic lights have just turned green after being red. The next time when traffic light A and B change from red to green at the same time will be _____ second later?

sxu0501 · 发表于 2016-11-21 13:57:38

630 sec??

sxu0501 · 发表于 2016-11-21 13:58:36

630 sec??

wyl11wyl · 发表于 2016-11-21 14:09:42

难道不是求90s 和75s 的最小公倍数？

windowshade · 发表于 2016-11-21 14:27:00

我的理解是：A每90秒后正好变绿，B每75秒正好变绿，问同时正好变绿要多少秒以后，就是求75和90的最小公倍数，5^2*3, 3^2*5*2->3^2*5^2*2=900

drunkpiano_v · 发表于 2016-11-21 16:53:44

should be 450 sec, 75和90的最小公倍数

[原始] 一道数学题的讨论

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