Posted by **Sherri** on Sunday, December 14, 2008 at 3:10pm.

If the probability of a swan drowning is 0.23, find the probability of exactly 4 out of the 7 swans drowning.

I think that the answer is:

(0.23)(0.23)(.00003404)= .000001801

is the right?

*round your answer to 3 significant digits*

- math- statistics -
**Damon**, Sunday, December 14, 2008 at 3:25pm
p of drowning = .23

1-p = prob of not drowning = .77

In general the probability of k hits in n trials is

C(n,k) p^k (1-p)^(n-k)

(binomial random variable )

so here we want

C(7,4)* .23^4 * .77^3

C(7,4) from Pascal's triangle of combination formula = 35

so

35 * .23^4 * .77^3 = .0447

- math- statistics -
**Sherri**, Sunday, December 14, 2008 at 7:28pm
thank you so much!!!

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