Maths S1 - Number of Arrangements of a word...

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Tealer
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Hi I am really puzzled by this, I had though I knew nCr and nPr but now I'm not so sure.

The question - "find the number of arrangements of the letters STATISTICS"

I thought it would be 10! but this is wrong as it is way over the value they give, I can only assume it must be divided by something, but its not as if you are choosing any letters so why should this be the case? I know its something to do with overcounting. I know this is probably really easy so please take the time to explain!! Many thanks!!
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Tealer
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Ok I've nailed it

10!/ (3! x 3! x 2!)

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waighty
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(Original post by Tealer)
Hi I am really puzzled by this, I had though I knew nCr and nPr but now I'm not so sure.

The question - "find the number of arrangements of the letters STATISTICS"

I thought it would be 10! but this is wrong as it is way over the value they give, I can only assume it must be divided by something, but its not as if you are choosing any letters so why should this be the case? I know its something to do with overcounting. I know this is probably really easy so please take the time to explain!! Many thanks!!
The key to it is to see if any of the letters repeat themselves, e.g. in "STATISTICS" 'S' repeats 3 times, 'T' repeats 3 times and 'I' repeats 2 times, hence you divide the total number of letters (i.e. 10) by 3!x3!x2!.
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Bhaal85
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(Original post by Tealer)
Hi I am really puzzled by this, I had though I knew nCr and nPr but now I'm not so sure.

The question - "find the number of arrangements of the letters STATISTICS"

I thought it would be 10! but this is wrong as it is way over the value they give, I can only assume it must be divided by something, but its not as if you are choosing any letters so why should this be the case? I know its something to do with overcounting. I know this is probably really easy so please take the time to explain!! Many thanks!!
Anybody got the S1 exam tomorrow?
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ickle_katy
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(Original post by Bhaal85)
Anybody got the S1 exam tomorrow?

nope but i have a probability exam next week on this!

love Katy ***
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Tealer
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Cheers waighty mate I have the S1 tommorow!! AAAAAH!!!
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lilsunflower
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(Original post by Tealer)
Hi I am really puzzled by this, I had though I knew nCr and nPr but now I'm not so sure.

The question - "find the number of arrangements of the letters STATISTICS"

I thought it would be 10! but this is wrong as it is way over the value they give, I can only assume it must be divided by something, but its not as if you are choosing any letters so why should this be the case? I know its something to do with overcounting. I know this is probably really easy so please take the time to explain!! Many thanks!!
This exact question was in a book I read. Umm.. basically you divide 10! by the number of repeats. i.e. if T is repeated 3 times, you divide by 3!...

The book is a blue one with "T1" written on it. It's really good.. that's what I felt anyway.
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