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combination

by teejaycrown » Sat Oct 20, 2012 12:00 pm
If a quality control check is made by inspecting a sample of 2 light bulbs from a box of 12 light bulbs, how many different samples can be chosen
6, 24, 36, 66, 72
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by Brent@GMATPrepNow » Sat Oct 20, 2012 12:11 pm
teejaycrown wrote:If a quality control check is made by inspecting a sample of 2 light bulbs from a box of 12 light bulbs, how many different samples can be chosen
6, 24, 36, 66, 72
We're choosing 2 lightbulbs from 12 lightbulbs.
Since the order in which the lightbulbs are selected does not matter, this can be handled using combinations.

So, we can select 2 lightbulbs from 12 lightbulbs in 12C2 ways ([spoiler]= 66 ways = D[/spoiler])

Aside: If anyone is interested, we have a free video on calculating combinations in your head: https://www.gmatprepnow.com/module/gmat-counting?id=789

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by teejaycrown » Sun Oct 21, 2012 5:15 pm
Thanks a lot for your help. Can we use the combination formula for this type of question:? in how many different ways can a group of 9 pole can be divided into 3 groups with each group containing 3 poeople.
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