# Probability - Combination Types

1. Assume you have ten (10) very expensive, leather bound books (all different authors) and you want to display these books on your fireplace mantle, but you are unsure how you want to arrange the books (by author, by height, year published, value . . . ). How many different ways can you arrange the books?

2. Assume you receive an advertisement in the mail for "mail order CDs". The company is offering you 4 CDs for one penny, followed by other purchases for the next year. There are 69 CDs to pick from. You determine from the 69 which 4 you want to purchase. How many different combinations are possible in this problem?

3. Finally, discuss the difference between these two problems (including the formulas [if any] used and differences in the applicable formulas).

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#### Solution Preview

1. The first book can be arranged in any one of the 10 places available. Having fixed the first book, the second book can be placed in any of the remaining 9 ...

#### Solution Summary

116 words to calculate two types of combination problems and explain key differences in the methods between them.