Max Z.

asked • 06/16/17

Find the probability of each event

A class has five boys and seven girls. If the teacher randomly picks five students, what is the probability that she will pick exactly two girls?

1 Expert Answer

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Kris V. answered • 06/16/17

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P{Exactly 2 girls out of 5 trials}
= C(7,2)C(5,3)/C(12,5)
=0.265
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Max Z.

Need to have it in a fraction
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06/16/17

Mark M.

Isn't a decimal a fraction?
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06/16/17

Kris V.

35/132
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06/16/17

Max Z.

How did you get that?
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06/16/17

Kris V.

OK, here are the details
 
P{Exactly 2 girls out of 5 trials}
= C(7,2)C(5,3)/C(12,5)
=[7!/(2! 5!)•(5!/(3!2!)] /[12!/(5!7!)]
=21•10/792
=210/792
=35/132.
 
There should be an option on your calculator for calculating C(n,r) and converting decimal to fraction.
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06/16/17

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