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# How many ways can 5 different colored marbles be placed in 3

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Joined: 01 Aug 2013
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How many ways can 5 different colored marbles be placed in 3  [#permalink]

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14 Oct 2013, 08:53
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Difficulty:

85% (hard)

Question Stats:

53% (01:31) correct 47% (01:36) wrong based on 230 sessions

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How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

(A) 60
(B) 90
(C) 120
(D) 150
(E) 180
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Joined: 10 Sep 2013
Posts: 79
Re: How many ways can 5 different colored marbles be placed in 3  [#permalink]

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15 Oct 2013, 02:19
4
1
How can we fill three pockets with 5 marbles?
3 + 1 + 1
2 + 2 + 1

With 3,1,1 distribution:
# of ways to select 3 from 5
5!/3!2! = 10
# of ways to select 1 ball from 2
2!/1! = 2
# of ways to select 1 ball from 1
1!/1! = 1
How many ways to distribute 3,1 and 1 to 3 boxes? 3!/2! = 3

10*2*3 = 60

With 2,2,1 distribution:
How many ways to select 2 from 5?
5!/2!3! = 10
# of ways to select 2 from 3
3!/2!1! = 3
# of ways to select 1 from 1
1
How many ways to distribute 2,2,1 to 3 boxes? 3!/2! = 3

10*3*3=90

90+60 = 150

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How many ways can 5 different colored marbles be placed in 3  [#permalink]

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20 Sep 2014, 13:22
3
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This is a tricky question! At least for people like me, who are from non-Quant background... I appreciate Igotthis's post but it appeared a little bit complicated to me (may be because I am not smart enough )

Anyway this is how I solved it...
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Re: How many ways can 5 different colored marbles be placed in 3  [#permalink]

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08 Aug 2015, 07:18
praffulpatel wrote:
How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

(A) 60
(B) 90
(C) 120
(D) 150
(E) 180

We have 5 marbles and 3 pockets
So we have two cases

Case-1: One Pocket with 3 marbles and two pockets with 1 marble each
No. of Arrangements = 5C3 * 3C1 * 2! = 10*3*2 = 60
5C3 - No. of ways of choosing 3 out of 5 marbles which have to go in one pocket
3C1 - No. of ways of choosing 1 out of 3 pockets in which 3 marbles have to go
2! - No. of ways of arranging remaining 2 marbles between remaining two pockets which get one marble each

Case-2: Two Pockets with 2 marbles each and one pockets with 1 marble
No. of Arrangements = 5C2 * 3C2 * 3C2 = 10*3*3 = 90
5C2 - No. of ways of choosing 2 out of 5 marbles which have to go in one pocket
3C2 - No. of ways of choosing 2 out of remaining 3 marbles which have to go in second pocket
3C2 - No. of ways of choosing 2 out of 3 pockets in each of which 2 marbles have to go

Total cases = 60+90 = 150

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Re: How many ways can 5 different colored marbles be placed in 3  [#permalink]

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09 Aug 2015, 14:23
GMATinsight, Bunuel, VeritasPrepKarishma,

I'm hoping one of you can explain why the 1-1-1 combination is ignored in answering this question. The question asks:
Quote:
How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

Would the answer not include 5P3? Since we can have at least 1 marble (i.e. exactly one marble) in each spot and the question does not specify that we must use all five of the marbles. Additionally, I think that permutation is the right way of counting for the 1-1-1 combination since a marble arrangement of Green-Blue-Red in pockets one-two-three is different from Blue-Red-Green in pockets one-two-three and so forth.
For the 1-1-1 combination, we will have: 5!/(5-3)! = 60 different arrangements.

Then we come to the 3-1-1 and 2-2-1 combinations.

For the 3-1-1 combination, in pocket one we can have any three of the five distinct marbles. The order inside one pocket doesn't matter. Therefore, we will use 5C3. For the 2nd pocket, we have two marbles left and we can only pick one because we must leave one for the third pocket. Therefore, we will use 2C1. And for the last (third) pocket we only have one choice. Now, we have 5C3, 2C1 and 1C1 in pockets one-two-three. These can be ordered in 3!/2! different ways because 2C1 = 1C1, and we have already counted the possibility of different colors in each pocket.
So for 3-1-1 combination, we have: 5C3 * 2C1 * 1C1 * 3!/2! = 60 different arrangements.

Similarly, for the 2-2-1 combination we have: 5C2 * 3C2 * 1C1 * 3!/2! = 90 different arrangements.

Finally, we will get 60+60+90 = 210 arrangements if we consider 1-1-1 to be a valid option - since the question does not explicitly exclude this possibility.

Could you please explain why we ignored 1-1-1 combination?
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Re: How many ways can 5 different colored marbles be placed in 3  [#permalink]

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10 Aug 2015, 00:18
1
jhabib wrote:
GMATinsight, Bunuel, VeritasPrepKarishma,

I'm hoping one of you can explain why the 1-1-1 combination is ignored in answering this question. The question asks:
Quote:
How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

Would the answer not include 5P3? Since we can have at least 1 marble (i.e. exactly one marble) in each spot and the question does not specify that we must use all five of the marbles. Additionally, I think that permutation is the right way of counting for the 1-1-1 combination since a marble arrangement of Green-Blue-Red in pockets one-two-three is different from Blue-Red-Green in pockets one-two-three and so forth.
For the 1-1-1 combination, we will have: 5!/(5-3)! = 60 different arrangements.

Then we come to the 3-1-1 and 2-2-1 combinations.

For the 3-1-1 combination, in pocket one we can have any three of the five distinct marbles. The order inside one pocket doesn't matter. Therefore, we will use 5C3. For the 2nd pocket, we have two marbles left and we can only pick one because we must leave one for the third pocket. Therefore, we will use 2C1. And for the last (third) pocket we only have one choice. Now, we have 5C3, 2C1 and 1C1 in pockets one-two-three. These can be ordered in 3!/2! different ways because 2C1 = 1C1, and we have already counted the possibility of different colors in each pocket.
So for 3-1-1 combination, we have: 5C3 * 2C1 * 1C1 * 3!/2! = 60 different arrangements.

Similarly, for the 2-2-1 combination we have: 5C2 * 3C2 * 1C1 * 3!/2! = 90 different arrangements.

Finally, we will get 60+60+90 = 210 arrangements if we consider 1-1-1 to be a valid option - since the question does not explicitly exclude this possibility.

Could you please explain why we ignored 1-1-1 combination?

Hey jhabib,

You have to place all the marbles. If you assume the 1-1-1 combination, note that 2 marbles are leftover. But you HAVE TO distribute 5 marbles. So 3-1-1 and 2-2-1 are the only possibilities. All 5 marbles must be distributed.
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How many ways can 5 different colored marbles be placed in 3  [#permalink]

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10 Aug 2015, 04:21
1
Hi jhabib

The Question has clearly specified that "ALL the Marbles have to be assigned to 3 pockets" so 1-1-1 needs to be ignored

Along with 1-1-1, 1-1-2, 1-2-1 ans 2-1-1 also need to be ignored.

I hope it helps!

jhabib wrote:
GMATinsight,

I'm hoping one of you can explain why the 1-1-1 combination is ignored in answering this question. The question asks:
Quote:
How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

Would the answer not include 5P3? Since we can have at least 1 marble (i.e. exactly one marble) in each spot and the question does not specify that we must use all five of the marbles. Additionally, I think that permutation is the right way of counting for the 1-1-1 combination since a marble arrangement of Green-Blue-Red in pockets one-two-three is different from Blue-Red-Green in pockets one-two-three and so forth.
For the 1-1-1 combination, we will have: 5!/(5-3)! = 60 different arrangements.

Then we come to the 3-1-1 and 2-2-1 combinations.

For the 3-1-1 combination, in pocket one we can have any three of the five distinct marbles. The order inside one pocket doesn't matter. Therefore, we will use 5C3. For the 2nd pocket, we have two marbles left and we can only pick one because we must leave one for the third pocket. Therefore, we will use 2C1. And for the last (third) pocket we only have one choice. Now, we have 5C3, 2C1 and 1C1 in pockets one-two-three. These can be ordered in 3!/2! different ways because 2C1 = 1C1, and we have already counted the possibility of different colors in each pocket.
So for 3-1-1 combination, we have: 5C3 * 2C1 * 1C1 * 3!/2! = 60 different arrangements.

Similarly, for the 2-2-1 combination we have: 5C2 * 3C2 * 1C1 * 3!/2! = 90 different arrangements.

Finally, we will get 60+60+90 = 210 arrangements if we consider 1-1-1 to be a valid option - since the question does not explicitly exclude this possibility.

Could you please explain why we ignored 1-1-1 combination?

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How many ways can 5 different colored marbles be placed in 3  [#permalink]

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06 Jan 2018, 13:02
praffulpatel wrote:
How many ways can 5 different colored marbles be placed in 3 distinct pockets such that any pocket contains at least 1 marble?

(A) 60
(B) 90
(C) 120
(D) 150
(E) 180

hi

I have seen a solution to a problem similar to this one elsewhere on the forum
let me explain it to you

5 different colored marbles can be placed in 3 distinct pockets without any restriction is

= 3^5 = 243

as we are asked to find out the ways in which any pocket must get at least 1 marble, lets find out the ways in which any pocket must not get at least 1 marble, and then subtract the number of ways in which any pocket must not get at least 1 marble from the total number of ways, that is 3^5

so lets get going

number of ways in which all marbles can get to 1 pocket is

= 3, as there are 3 distinct pocket in total

now, number of ways in which 2 pockets can get all the marbles and 1 pocket remains empty is

= (2^5 - 2) * 3 = 90

2 has been subtracted to eliminate the possibility that any pocket out of 2 can get all the marbles

3 has been multiplied with the whole expression, because 2 pockets out of 3 have been selected

= 243 - 90 - 3

= 150 (D)

hope this helps
thanks

cheers, and do consider some kudos, man
How many ways can 5 different colored marbles be placed in 3 &nbs [#permalink] 06 Jan 2018, 13:02
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