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# A box has 10 balls. Find how many ways 6 balls can be

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Intern
Joined: 05 Jun 2004
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A box has 10 balls. Find how many ways 6 balls can be [#permalink]  02 May 2005, 06:12
A box has 10 balls. Find how many ways 6 balls can be selected if each ball may be repeated any number of times.
Manager
Joined: 22 Apr 2005
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General formula for selection with repetitions.

The number of ways to pick k items out of n with repetitions = kC(n+k-1)

In this case

6C(10+6-1) = 6C15
Intern
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is there a simpler way of doing this? not able to understand the formula..
Director
Joined: 31 Aug 2004
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If all selections are independant from each other I would prefer 10^6
Manager
Joined: 22 Apr 2005
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Economiser wrote:
is there a simpler way of doing this? not able to understand the formula..

This is a simple way.
Here is an article for you
Senior Manager
Joined: 19 Sep 2004
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Tyr wrote:
Economiser wrote:
is there a simpler way of doing this? not able to understand the formula..

This is a simple way.
Here is an article for you

I find it little difficult to comprehend can someone please exaplain!

Saurabh Malpani
Senior Manager
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MA wrote:
gmat2me2 wrote:
twixt wrote:
If all selections are independant from each other I would prefer 10^6

Isnt that 6^10??

i also think so.

can you please how ur working.
Director
Joined: 31 Aug 2004
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gmat2me2 wrote:
twixt wrote:
If all selections are independant from each other I would prefer 10^6

Isnt that 6^10??

I have to select 6 balls among 10, so first one 10 choices, replacement, second one 10 choices...

That is why I answered 10^6...
Intern
Joined: 05 May 2005
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I think the answer should be:10*9*8*7*6*5,is that right?
Director
Joined: 31 Aug 2004
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Maybe an old prob Pro could provide some insight to this one...
VP
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olivebaby wrote:
I think the answer should be:10*9*8*7*6*5,is that right?

Hi, because being able to repeated, each ball has the same probability of being selected.

Hence repeat 6 times: 10 * 10 *10... = 10^6
Director
Joined: 18 Feb 2005
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twixt wrote:
gmat2me2 wrote:
twixt wrote:
If all selections are independant from each other I would prefer 10^6

Isnt that 6^10??

I have to select 6 balls among 10, so first one 10 choices, replacement, second one 10 choices...

That is why I answered 10^6...

Yes Twixt...It is 10^6.....
Director
Joined: 31 Aug 2004
Posts: 610
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Thx, During a fraction of second I had the feeling I had lost all my probs concepts !!
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