Let S = {1,2,3,4,5}

(a) List all the 3-permutations of S

(a) List all the 3-combinations of S

Can any one help me with this ??

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- Nov 17th 2008, 09:29 AMbhuvanCounting problem
Let S = {1,2,3,4,5}

(a) List all the 3-permutations of S

(a) List all the 3-combinations of S

Can any one help me with this ?? - Nov 17th 2008, 11:12 AMTitaniumX
a) 5C3 = 5!/(3!*(5-3)!) = 10 (order doesn't matter)

b) 5P3 = 5!/(5-3)! = 60 (order matters)

a)

{1,2,3}

{1,2,4}

{1,2,5}

{1,3,4}

{1,3,5}

{1,4,5}

{2,3,4}

{2,3,5}

{2,4,5}

{3,4,5}

Total = 10

b)

{1,2,3}

124

125

132

134

135

142

143

145

152

153

154

.

.

.

should add up to 60 - Nov 17th 2008, 12:33 PMSoroban
Hello, bhuvan!

Quote:

Let

(a) List all the 3-permutations of

I'll start the list . . .

. .

Quote:

(b) List all the 3-combinations of

. . .

Edit: . Ha! TitaniumX beat me to it . . .

. - Nov 17th 2008, 01:58 PMbhuvan
thank you very much ...

How many solutions are there to the equation

x1+x2+x3+x4=17

where x1,x2,x3 and x4 are nonnegative integers ??

appreciate your reply. - Nov 17th 2008, 02:24 PMPlato
- Nov 17th 2008, 04:10 PMbhuvan
can you please give me one example of that ??