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Jerry W. Lewis Jerry W. Lewis is offline
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Default calculating probabilty of x number of successes with multiple tria

You have not provided enough information to answer the question. What
follows assumes that the trials are independent.

There are 352716=COMBIN(21,10) different ways to get 10 successes from 21
trials. You could enumerate them and sum the probability of each. For
example, the probability that the first 10 trials are successes and the rest
failures would be 3E-09, as calculated by the array formula
=PRODUCT(B2:B11)*PRODUCT(1-B12:B22), assuming that the stated probabilities
are in B2:B22. Of course this approach would be exceptionally tedious and
time consuming.

If it were my homework assignment, I would review properties of probability
generating functions
http://en.wikipedia.org/wiki/Probabi...ating_function
and use 0.05=BINOMDIST(10,21,HARMEAN(B2:B22),FALSE) as a crude ball-park
estimate to ensure that I had done the work correctly

Jerry

"mk9999999" wrote:


how do i calculate the probability of a certain number of successes when
there are multiple trials each with different probabilities e.g.

Trial P (of success)
1 0.2
2 0.4
3 0.9
4 0.6
5 0.5
6 0.4
7 0.7
8 0.3
9 0.1
10 0.5
11 0.6
12 0.7
13 0.9
14 0.1
15 0.2
16 0.2
17 0.2
18 0.5
19 0.6
20 0.7
21 0.9

How would i calculate the probability of 10 successes for example?

I could calculate it manually, but there must be a quicker way of doing it
using excel?

cheers