math statistics
posted by Sherri .
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*

p of drowning = .23
1p = prob of not drowning = .77
In general the probability of k hits in n trials is
C(n,k) p^k (1p)^(nk)
(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 
thank you so much!!!

If the probability of a lame leaping lord is 0.24