Question 308256: Please can someone help explain how to do this. I have tried to do this but I keep getting stuck. I keep getting numbers like 2.45E+10. I have lots of these to do and cannot figure out how to do these. Thanks.
A die is rolled 20 times and the number of twos that come up is tallied. Find the probability of getting the given result. More than three twos.
A) .564
B) .433
C) .905
D) .403
Answer by scott8148(6628)   (Show Source):
You can put this solution on YOUR website! this is a binomial probability ___ t is two, n is not two
P(t) = 1/6 ___ P(n) = 5/6
the easiest method is to find the probabilities of 0, 1, 2, and 3 twos; and subtract those from one
it is the first four terms of the binomial expansion {[P(n)] + [P(t)]}^20
[P(n)]^20 + (20C1){[P(n)]^19 * [P(t)]} + (20C2){[P(n)]^18 * [P(t)]^2} + (20C3){[P(n)]^17 * [P(t)]^3}
just a comment ___ the "expected" number is (20 * 1/6) or (3 1/3)
___ from the choice of answers, A looks good
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