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Combinations with x !!

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Manager
Manager
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Joined: 03 Aug 2018
Posts: 66
Location: India
Concentration: Strategy, Operations
GMAT 1: 590 Q45 V26
GPA: 3.5
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Combinations with x !!  [#permalink]

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New post 16 Oct 2018, 07:28
Dear All

Please can you help me understand how below combination can be resolved i.e. xC4!

I did using xC4! = x!/ ( x-4)!*4!
then x! can be expanded as x(x-1)(x-2)(x-3)(x-4)! / ( x-4)! *4! and then solve it.

Is this approach correct, maths still is my learning area ..

Question Source : https://gmatclub.com/forum/how-many-peo ... 50290.html
Director
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G
Joined: 19 Oct 2013
Posts: 520
Location: Kuwait
GPA: 3.2
WE: Engineering (Real Estate)
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Re: Combinations with x !!  [#permalink]

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New post 16 Oct 2018, 14:40
1
Hello what you have done is correct however in that particular case it is a data sufficiency question. The expansion and solving is not necessary to proceed with.

say xC4 from this you can find the x (this is from statement 2)

You know from this tedious expansion that you will find the number of customers.

Now that you know x and you know that one out of every 6 purchases.

So you have a clear answer once combined.

I hope this helps.
Manager
Manager
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B
Joined: 03 Aug 2018
Posts: 66
Location: India
Concentration: Strategy, Operations
GMAT 1: 590 Q45 V26
GPA: 3.5
GMAT ToolKit User
Re: Combinations with x !!  [#permalink]

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New post 16 Oct 2018, 20:12
Salsanousi wrote:
Hello what you have done is correct however in that particular case it is a data sufficiency question. The expansion and solving is not necessary to proceed with.

say xC4 from this you can find the x (this is from statement 2)

You know from this tedious expansion that you will find the number of customers.

Now that you know x and you know that one out of every 6 purchases.

So you have a clear answer once combined.

I hope this helps.


Thank You Salsanousi :)

Indeed you are right and we do not need to solve the tedious question.

Had posted my query to seek advice on my approach to solve xC4! and you have helped me, thank you

Good Luck :)
Abhinav
GMAT Club Bot
Re: Combinations with x !!   [#permalink] 16 Oct 2018, 20:12
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