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This is for an independent study class. I am basically teaching myself various math subjects that we don't get in school.

here it is:

Four letters are chosen at random from the word MISSISSIPPI. Determine the probability that at least three I's are chosen.

now I know the answer should be (29/330) according to my book, but I can't come up with this answer.

It seems to me that the logical thing would be to do this:

(4/11)*(3/10)*(2/9)*(1/8)= (1/330) the probability of getting all I's

then

(4/11)*(3/10)*(2/9)*(1-(1/8))= (7/330)

(7/330)+(1/330)= (8/330)= (4/165)

I've tried many other things to come up with (29/330) but I can't get that answer

any help would be greatly appreciated.