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Of the 100 students at a certain school, 30 students are [#permalink]
02 Sep 2004, 15:13
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Of the 100 students at a certain school, 30 students are taking a chemistry class, 40 students are taking a physics class, and 20 students are taking both a physics and a chemistry class. If a student is chosen at random from the school, what is the probability that he or she is taking a physics or a chemistry class?
With Venn Diagram, you have: 10 only chemistry 20 only physics 20 chemistry&physics
Odds are 1/2 of students will be taking either physics or chemistry A it is
Paul, isn't the question asking for "probability that he or she is taking a physics or a chemistry class" and you answered for "probability that he or she is taking a physics or a chemistry class or both"
I think it might be 10+20/100 = 3/10 (Choice B)
Am I reading too much?
hardworker, there are students taking physics only, chemistry only, and students taking both subjects.
If you pick a student and he/she (bad english here, don't use he/she for verbal !) is taking either physics or chemistry, that student can belong to anyone group. We need to ask are the two events mutually exclusive ? Yes. Because there are students who do both subjecs.
So the way to do this is P(A) + P(B) - P(A intersect B)