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pls explain this too...?? so much confused

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pls explain this too...?? so much confused [#permalink] New post 09 Mar 2011, 03:29
can someone pls explain this concept..?
what do we mean by order does matter and order does not matter...??
for eg..) if we need to know the seating arrangement for 4 persons from 7 chairs,,,we take order matters and if we need to make a team of 4 people from 7 people in a room we take order not matters....??

or is there a better method to identify when order matters and when order does not matters...??
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Re: pls explain this too...?? so much confused [#permalink] New post 09 Mar 2011, 03:46
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There is a group of 7 people and 4 chairs are available. You want to seat 4, then the order matters
First chair can be filled in 7 ways
Second chair can be filled in 6 ways
Third chair can be filled in 5 ways
Fourth chair can be filled in 4 ways
Total ways = 7 * 6 * 5 * 4

On the other hand, if you are making a team of 4 from a group of 7, order does not matters. Its 7C4
A = First person can be chosen in 7 ways
B = Second person - 6 ways
C = Third person - 5 ways
D = Fourth person - 4 ways

But ABCD = BCDA = CDAB = DABA ..... etc
So you have duplicates. There will be 4! duplicates per selection

To make unique teams, you will have to divide by 4!
Hence no of ways = 7 * 6 * 5 * 4 / (4!) = 7C4

punyadeep wrote:
can someone pls explain this concept..?
what do we mean by order does matter and order does not matter...??
for eg..) if we need to know the seating arrangement for 4 persons from 7 chairs,,,we take order matters and if we need to make a team of 4 people from 7 people in a room we take order not matters....??

or is there a better method to identify when order matters and when order does not matters...??
Re: pls explain this too...?? so much confused   [#permalink] 09 Mar 2011, 03:46
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pls explain this too...?? so much confused

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