In: Statistics and Probability
The probability that a committee has all seventh graders is 0.012
#################Explanation ######################
Note that here order of graders in committee does not matter.
The total number of grader :
Since there are 6 ninth graders, 11 eighth graders, and 10 seventh graders
N = 27
The total numbers of committees can form is C(27,4)
n(N) =
=17550
From 10 seven grader we can choose C(10,4) different groups of 4 seven grader
Let n(X) be the number of the committees has all seventh graders,
The number of the committees has all seventh graders
is C(10,4)
n(X) =
= 210
The probability that a committee has all seventh graders is
=
= 0.011965 ~0.012
The probability that a committee has all seventh graders is 0.012
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10! 4!
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C(10,4) C(27,4) 210 17550