# probability word problems

A college Calculus 1 course with 15 (20) who have (had) some(none) calculus in high school & probability of 3/10 (1/10) of making an "A" in Calculus 1. Some student earns "A", what is the probability of said student had some calculus in high school?

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What information do we have?

P(Had Calc) = 15/35
P(Gets A | Had Calc) = 3/10
P(Gets A | Not Had Calc) = 1/10


So we can use P(A|B) = P(B|A)*P(A)/P(B) like so:

P(Had Calc | Gets A) = P(Gets A | Had Calc) * P(Had Calc) / P(Gets A)


We still need P(Gets A), but I'm sure you can figure that out.

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Do you mind walking me thru this problem to make sure I got the correct answer? – kimj Sep 29 '12 at 20:51