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In how many ways can 5 different colored marbles be placed in 3 distin

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In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 14 Oct 2013, 07:53
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A
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Question Stats:

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

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New post 15 Oct 2013, 01:19
4
2
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

Answer: 150. D
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 20 Sep 2014, 12:22
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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 :lol: )

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

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New post 08 Aug 2015, 06:18
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

Answer: option D
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 09 Aug 2015, 13:23
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: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 09 Aug 2015, 23:18
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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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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 10 Aug 2015, 03:21
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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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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 06 Jan 2018, 12:02
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

now we are in business

the answer is

= 243 - 90 - 3

= 150 (D)

hope this helps
thanks

cheers, and do consider some kudos, man
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 09 Oct 2018, 22:13
VeritasKarishma wrote:
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.


Dear Karishma ..
I am bitterly confused with this problem . I doubt the approach or the problem has some defect . Please correct me if I am wrong .
All the approaches are considering 3 bags as identical , but in problem they are distinct .
My approach to this problem :
I am considering 5 different marbles a b c d e and 3 different bags 1 2 3 .
So first distribute 3 balls one ball each to each bag .
select 3 balls to distribut 5C3 and then distribute to 3 different bags in 3! ways .
so total 60 ways .
Now we are left with 2 balls and 3 bags each containing one ball each .
for first ball we have 3 options and second ball again 3 options . 3*3 ways .
TOTAL = 60*3*3=540 ways .

Please somebody help me in this . This problem just made me mad .. :P
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 09 Oct 2018, 23:22
karnaidu wrote:
Dear Karishma ..
I am bitterly confused with this problem . I doubt the approach or the problem has some defect . Please correct me if I am wrong .
All the approaches are considering 3 bags as identical , but in problem they are distinct .
My approach to this problem :
I am considering 5 different marbles a b c d e and 3 different bags 1 2 3 .
So first distribute 3 balls one ball each to each bag .
select 3 balls to distribut 5C3 and then distribute to 3 different bags in 3! ways .
so total 60 ways .
Now we are left with 2 balls and 3 bags each containing one ball each .
for first ball we have 3 options and second ball again 3 options . 3*3 ways .
TOTAL = 60*3*3=540 ways .

Please somebody help me in this . This problem just made me mad .. :P


You have some double counting here. When you select some from a group and distribute and then distribute the rest to the same bags/pockets, there is double counting.

Say you distributed a, b, c first such that
Bag1 had a
Bag2 had b
Bag3 had c
Then you distributed d and e such that Bag1 got d and bag2 got e.

Take another case.
Say you distributed d, b and c first such that
Bag1 had d
Bag2 had b
Bag3 had c
Then you distributed a and e such that Bag1 got a and bag2 got e.

Note that both cases have exactly the same end result. But you would count them as two separate cases. Similarly, there will be other cases which will be double counted. Hence this method will not work.
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 09 Oct 2018, 23:53
sxyz wrote:
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 :lol: )

Anyway this is how I solved it...



Hii ..
In this approach you are missing arrangement of bags . You have to take care of that too ..
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Re: In how many ways can 5 different colored marbles be placed in 3 distin  [#permalink]

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New post 18 Oct 2018, 10:16
Hi. I don't understand why this has been multiplied by 3!/2! for 2-2-1 combination. Plus, shouldn't 5c2*3c2 be multiplied by 2! as the pockets are distinct, and the arrangement would matter? Thanks
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Re: In how many ways can 5 different colored marbles be placed in 3 distin &nbs [#permalink] 18 Oct 2018, 10:16
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