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Im trying to calculate the chance or probability of number 75 appearing. I have total 100 rows in microsoft excel and have frequency of number 75. Each row contains 3 cells and each cell contains a random number between 1-100. For example typical table cells:

75 23 01
91 64 67
05 12 75

Im trying to use the formula:

P(k out of N) = (N! / (k!(N-k)!)) * (pk)(qN-k)

where:

N = 100 Total rows
k = 15 Number of times number 75 appears in these 100 rows
p = ?
q = 1 - q

Im stuck on calculating p.

Notes: numbers never repeat in the same cell. meaning there will never be a case like:

 75 75 22
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1 Answer 1

up vote 1 down vote accepted

If the numbers are random, the probability of $75$ appearing in any one row is $0.03$. That is your $p$. This counts on the fact that numbers are not repeated within a row.

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why 0.03? they are random but the range is between 1-100 it cant be 101 –  GGio Jul 11 '13 at 20:07
    
Yes, you are selecting 3 numbers out of 100, so the chance that any given number is selected is 0.03. If you had one number per row it would be 0.01, for 3 (taken without replacement) it is 0.03. –  Ross Millikan Jul 11 '13 at 20:09
    
so if instead 100 rows the range would be 121 then it would be what how would I calculate it? right now its 100 but what if later I would want to increase it –  GGio Jul 11 '13 at 20:09
    
It would be 3/121 then. –  Ross Millikan Jul 11 '13 at 20:10
    
got it, thank you, the other variables are correct? the way im calculating it –  GGio Jul 11 '13 at 20:11
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