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#1 Re: Help Me ! » binary sequences 5 from 9 how many combinations? » 2012-07-28 18:00:29

Thanks Bobby, video is good

Thanks Bob, that is good way of thinking about the problem

#3 Re: Help Me ! » binary sequences 5 from 9 how many combinations? » 2012-07-28 04:19:36

OK, thanks Bobby.

I am trying to get me head around the calculation but in the meantime I will take your word for it!

Is there a link to somewhere that has an explanation of why that factorial ratio/product is the right answer?

#4 Re: Help Me ! » binary sequences 5 from 9 how many combinations? » 2012-07-28 03:30:27

actually no
4 in 9 and 5 in 9 are the same problem so the anser is

1 in 9 answer is 9
2 in 9 answer is 8 x 7
3 in 9 answer is 7 x 6 x 5
4 in 9 answer is 6 x 5 x 4 x 3 (same as 5 in 9)

(= 6!/2! ?)
= 360

?

#5 Help Me ! » binary sequences 5 from 9 how many combinations? » 2012-07-28 02:23:02

mojorising
Replies: 11

Hi

I can't remeber how to do this. It has got something to do with factorials i think.

I want to know how many combinations there are for a 9 digit binary sequence where 5 of the bits must be 1 and 4 of the bits must be 0

e.g.

111110000
111101000
111100100
111100010
111100001
111010001
111001001
...
....

etc.

Can anybody tell me the answer and also possibly how the calculation is done?

Thanks?

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