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A school dance committee of four people is selected at random from a group of 9 ninth graders, 8 eighth graders, and 10 seventh graders. What is the probability that the committee has all seventh graders? The probability that the committee has all seventh graders is?

NOTE: I realize that this is a combination problem with 10C4 as the set up. But my question is how would I go about multiplying and dividing this out into a fraction? I am a new learner to permutations and combinations.

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  1. how many 4 person committees can be selected from the 27 students
    ... 27C4

    how many 4 person committees can be selected from the 10 7th graders
    ... 10C4

    probability of all 7th graders ... 10C4 / 27C4

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