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 Post subject: Combinatorics and Probability (Vol. XII) page23Posted: Mon Dec 06, 2010 11:38 pm

Joined: Thu Oct 21, 2010 5:19 am
Posts: 16
Dear vp_help,

There are no answers offered by the book. I want to sure whether I am right of these question.Would you please check it for me? Many thanks again!

-"1.How many different collections of 4 books can Mary taken on vacation if she has 20 books to choose from?"

20!/4!(20-4)!

-"2.In how many ways can 20 books be arranged on a shelf?"
20!

-"3.At a race,how many different orderings are possible for 1st,2nd,and 3rd place if the race has 20 participants?"
12!/(12-3)!

-"4.How many subcommittees of 4 are possible from committee of 12 people?"

12!/4!(12-4)!

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 Post subject: Re: Combinatorics and Probability (Vol. XII) page23Posted: Tue Dec 07, 2010 5:22 pm

Joined: Thu Feb 12, 2009 6:32 pm
Posts: 497
Cathy,

Please see comments inserted in-line below. I have overwritten some of your original answers.

- Veritas Help

-"1.How many different collections of 4 books can Mary taken on vacation if she has 20 books to choose from?"

20!/( 4!(20-4)! ) -- correct

-"2.In how many ways can 20 books be arranged on a shelf?"
20! ... correct

-"3.At a race,how many different orderings are possible for 1st,2nd,and 3rd place if the race has 20 participants?"
20 * 19 * 18 ... correct

-"4.How many subcommittees of 4 are possible from committee of 12 people?"

12!/( 4!(12-4)!) ... correct

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 Post subject: Re: Combinatorics and Probability (Vol. XII) page23Posted: Wed Dec 08, 2010 12:57 am

Joined: Thu Oct 21, 2010 5:19 am
Posts: 16
Thanks.Your answers always give me the courage to go on!

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