Question 737654: two numbers are selected at random from 1 to 9 find the probability that their sum is even?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! two numbers are selected at random from 1 to 9 find the probability that their sum is even?
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Consider a 9 by 9 array of these pairs.
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Consider the sum of each of the 81 pairs in the array.
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The 1st row of sums looks like: 2,3,4,5,6,7,8,9,10::::: 5 even : 5 odd
the 2nd row of sums looks like: 3,4,5,6,7,8,9,10,11:::: 4 even : 5 odd
The 3rd row of sums looks like: 4,5,6,7,8,9,10,11,12::: 5 even : 5 oddc.
etc
etc
etc
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# of even sums is 5+4+5+4+5+4+5+4+5 = 41
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P(sum is even) = 41/81
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Cheers,
Stan H.
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