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math challenge II-A combinatorics 9.22

 
 
WuZeyin的头像
math challenge II-A combinatorics 9.22
WuZeyin - 2021年10月5日 Tuesday 07:01
 

The answer sheet didn't give an answer. This is strange. What is the answer to this problem? Is it 7 over 9?

Thanks,

 
LensmireJohn的头像
Re: math challenge II-A combinatorics 9.22
LensmireJohn - 2021年10月5日 Tuesday 11:34
 

The probability should be 5 / 9 here. Consider the drawing below of the 3 by 3 grid which plots the arrival times of Jack and George:


5 of the 9 regions are shaded, hence the probability 5/9.

 
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