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Combination?

by elliefrance » Thu Sep 20, 2012 6:44 pm
Q: If a quality control check is made by inspecting a sample of 2 lightbulbs from a box of 12 lightbulbs, how many different samples can be chosen?

6
24
36
66
72

Thanks!
-Ellie
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Source: — Data Sufficiency |

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by Anurag@Gurome » Thu Sep 20, 2012 7:41 pm
elliefrance wrote:Q: If a quality control check is made by inspecting a sample of 2 lightbulbs from a box of 12 lightbulbs, how many different samples can be chosen?

6
24
36
66
72

Thanks!
-Ellie
No. of possible ways of choosing 2 lightbulbs from a box of 12 lightbulbs = 12C2 = 12!/(2!)(12 - 2)! = 12!/(2!)(10!) = (12 * 11)/2 = 6 * 11 = 66

The correct answer is D.
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