# Perms and combs question

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#1

How would I do these?
0
3 years ago
#2
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).
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#3
(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?
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3 years ago
#4
(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.
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#5
(Original post by ghostwalker)
Yes, to i and ii.
ok thanks.
For iii) would it be 200X(184754/184756) + 100X(2/184756) ?
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3 years ago
#6
(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.
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#7
(Original post by ghostwalker)
Close; but why have you put 200 and 100? Check that.
oops

I meant 100 and 50
0
3 years ago
#8
(Original post by SWISH99)
oops

I meant 100 and 50
It's correct now
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