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How many ways can one choose 20 cookies from 45 different types (assuming there are at least 20 of each type)?(a) ^64C21 * 15(b) ^64C20(c) ^44C20 * 2!(d) ^65C22This question was posed to me in quiz.Query is from Counting in portion Counting of Discrete Mathematics

Answer»

Correct answer is (b) ^64C20

To explain I would say: IMAGINE the 20 cookies ONE is choosing are indistinguishable dots. The 45 different types of cookies are like 45 DISTINGUISHABLE boxes and so the answer is C(45 + 20-1, 20) = ^64C20.



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