How many different samples can be chosen???

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gmatpup: Senior | Next Rank: 100 Posts; Posts: 88; Joined: Sat Oct 15, 2011 6:38 pm; Thanked: 1 times; Followed by:1 members

How many different samples can be chosen???

by gmatpup » Sat Dec 24, 2011 9:29 am

If a quality control check is made by inspecting a sample of 2 lightbuls from a box of 12, how many different samples can be chosen?

A. 6
B. 24
C. 36
D. 66
E. 72

Answer is D

Please explain, thank you

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Source: Beat The GMAT — Problem Solving | Sat Dec 24, 2011 9:29 am

LalaB: Master | Next Rank: 500 Posts; Posts: 425; Joined: Wed Dec 08, 2010 9:00 am; Thanked: 56 times; Followed by:7 members; GMAT Score:690

by LalaB » Sat Dec 24, 2011 9:35 am

12C2 =12!/2!*10!=66

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pm; Location: Milpitas, CA; Thanked: 1854 times; Followed by:523 members; GMAT Score:770

by Anurag@Gurome » Sun Dec 25, 2011 7:43 pm

gmatpup wrote:If a quality control check is made by inspecting a sample of 2 lightbuls from a box of 12, how many different samples can be chosen?

A. 6
B. 24
C. 36
D. 66
E. 72

Answer is D

Please explain, thank you !

Samples can be chosen in 12C2 = 12!/[2! * (12 - 2)!] = (12 * 11 * 10!)/[2 * 10!]
= 6 * 11 = 66

The correct answer is D.

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Gurome, Inc.
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ArunangsuSahu: Master | Next Rank: 500 Posts; Posts: 382; Joined: Thu Mar 31, 2011 5:47 pm; Thanked: 15 times

by ArunangsuSahu » Tue Jan 03, 2012 9:55 pm

12C2=66

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8088; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Tue Jun 26, 2018 5:16 pm

gmatpup wrote:If a quality control check is made by inspecting a sample of 2 lightbuls from a box of 12, how many different samples can be chosen?

A. 6
B. 24
C. 36
D. 66
E. 72

The number of samples that can be chosen is:

12C2 = 12!/(2! x 10!) = (12 x 11)/2! = 66

Answer: D

Scott Woodbury-Stewart
Founder and CEO
[email protected]