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Perms and combs question

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How would I do these?
The mouse's movements are a sequence of 10 'right' movements and 10 'up' movements. So you need to find the number of ways by using permutations. [You have RRR...RRUUU..UUUU. (10 R's and 10 U's) -> what are the ways of arranging these?]

Part (iii) is linked to part (ii).
Reply 2
Original post by BobbJo
The mouse's movements are a sequence of 10 'right' movements and 10 'up' movements. So you need to find the number of ways by using permutations. [You have RRR...RRUUU..UUUU. (10 R's and 10 U's) -> what are the ways of arranging these?]

Part (iii) is linked to part (ii).


so for i) I got 20!/(10!10!)

how would I do ii) wouldnt it just be 1 over my answer for i) for both?
Original post by SWISH99
so for i) I got 20!/(10!10!)

how would I do ii) wouldnt it just be 1 over my answer for i) for both?


Yes, to i and ii.
Reply 4
Original post by ghostwalker
Yes, to i and ii.

ok thanks.
For iii) would it be 200X(184754/184756) + 100X(2/184756) ?
Original post by SWISH99
ok thanks.
For iii) would it be 200X(184754/184756) + 100X(2/184756) ?


Close; but why have you put 200 and 100? Check that.
(edited 6 years ago)
Reply 6
Original post by ghostwalker
Close; but why have you put 200 and 100? Check that.


oops

I meant 100 and 50
Original post by SWISH99
oops

I meant 100 and 50


It's correct now :smile:

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