In how many different ways can 3 identical green shirts and

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ktrout2020: Senior | Next Rank: 100 Posts; Posts: 41; Joined: Wed Oct 30, 2019 1:10 pm

by ktrout2020 » Sun Nov 03, 2019 10:41 am

In how many different ways can 3 identical green shirts and 3 identical red shirts be distributed among 6 children such that each child receives a shirt?

A. 20
B. 40
C. 216
D. 720
E. 729

Source: Magoosh

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Source: Beat The GMAT — Problem Solving | Sun Nov 03, 2019 10:41 am

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Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 amFollowed by: 34 members; Location: Grand Central / New York; Thanked: 470 times

by Jay@ManhattanReview » Mon Nov 04, 2019 1:06 am

ktrout2020 wrote:In how many different ways can 3 identical green shirts and 3 identical red shirts be distributed among 6 children such that each child receives a shirt?

A. 20
B. 40
C. 216
D. 720
E. 729

Source: Magoosh

This is a question on arranging objects of which few of them are indistinguishable/identical objects.

Say there are a total of n objects; out of which there are p identical objects, q identical objects, and r identical objects.

Thus, the no, of ways, n objects can be arranged = n! / (p!*q!*r!)

Let's switch to the question:

There are 6 shirts; thus, n = 6; out of 6 shirts, there are 3 identical green shirts; thus, p = 3. Similarly, there are 3 identical red shirts, q = 3.

Thus, the no. of ways 6 shirts can be distributed = 6! / (3!*3!) = 20.

The correct answer: A

Hope this helps!

-Jay
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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Mon Nov 04, 2019 4:22 am

ktrout2020 wrote:In how many different ways can 3 identical green shirts and 3 identical red shirts be distributed among 6 children such that each child receives a shirt?

A. 20
B. 40
C. 216
D. 720
E. 729

Source: Magoosh

From 6 children, the number of ways to choose 3 to receive green shirts = 6C3 = (6*5*4)/(3*2*1) = 20.
From the 3 remaining children, the number of ways to choose 3 to receive red shirts = 3C3 = (3*2*1)/(3*2*1) = 1.
To combine these options, we multiply:
20*1 = 20.

The correct answer is A.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Mon Nov 04, 2019 5:38 am

ktrout2020 wrote:In how many different ways can 3 identical green shirts and 3 identical red shirts be distributed among 6 children such that each child receives a shirt?

A. 20
B. 40
C. 216
D. 720
E. 729

Source: Magoosh

We can take this question and ask an easier question: In how many ways can we choose 3 of the 6 children to receive a green shirt?

Notice that, once we have given a green shirt to each of those 3 chosen children, the REMAINING 3 children must get red shirts. In other words, once we have given green shirts to 3 children, the children who get red shirts is locked.

So, in how many ways can we select 3 of the 6 children to receive a green shirt?
Since the order of the selected children does not matter, this is a combination question.
We can choose 3 children from 6 children in 6C3 ways (= 20 ways)

Answer: A

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8139; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Wed Nov 06, 2019 7:13 pm

ktrout2020 wrote:In how many different ways can 3 identical green shirts and 3 identical red shirts be distributed among 6 children such that each child receives a shirt?

A. 20
B. 40
C. 216
D. 720
E. 729

Source: Magoosh

The number of ways to distribute the shirts to the children is given by the number of arrangements of:

G - G - G - R - R - R

Since we have 6 total letters and 3 repeated G's and 3 repeated R's, we can arrange the letters in the following number of ways, using the indistinguishable permutations formula:

6!/(3! x 3!) = (6 x 5 x 4)/(3 x 2) = 5 x 4 = 20.

Answer: A

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