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| Teaching Since: | May 2017 |
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MBA (IT), PHD
Kaplan University
Apr-2009 - Mar-2014
Professor
University of Santo Tomas
Aug-2006 - Present
I broke the question down into 2 parts, then solved them and multiplied the answer to get 11,880 ways.
We can solve this by breaking down the question into 2 smaller questions. The first question is "how many ways can we choose 4 chairs out of 12 to have someone sit in" and the second question is "how many ways can 4 people sit in 4 chairs". Our final answer will be the product of the 2 smaller questions.
The first smaller question - "how many ways can we choose 4 chairs out of 12 to have someone sit in" - is a combinations question (how many ways can we pick 4 chairs from a group of 12) - that is written in a few different notations - I'll write it out as Combination 12 choose 4 and in notation C12,4
For each combination of 4 chairs selected out of the 12, there are different ways the people can sit in them - we can have persons A B C D, or A B D C, etc. There are, in fact 4!
ways each selection of chairs can be sat in.
Our final answer, therefore is
(4!)(C12,4)
Let's solve
(4!)=4â‹…3â‹…2â‹…1=24
(C12,4)=12!(4!)(8!)=12â‹…11â‹…10â‹…9â‹…8!(24)(8!)=12â‹…11â‹…10â‹…924
Now let's combine the 2:
(24)(12â‹…11â‹…10â‹…924)=(12â‹…11â‹…10â‹…9)=11,880
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