Posted by mysterychicken on Thursday, June 25, 2009 at 6:05pm.
Need help with these
1.How many groups of 4 fabrics can be selected from 7 fabrics?
2.The school photographer wants to photograph 3 students from a club with 14 members. How many combinations can be made?
3.Philip wishes to check 2 books out of his school library. If the library contains 800 books, in how many ways might Philip make his choice of books?
Thanks
MC

PreAlgebra [Combinations]  Damon, Thursday, June 25, 2009 at 6:21pm
C(n,k) = n!/[ (nk)!k! ]
for example if n = 7 and k = 4
C(7,4) = 7! /[ 3! 4! ]
= 7*6*5 *4! /[3*2*1 *4!]
4! cancels top and bottom
6 cancels top and bottom
= 7*5
=35
Now try n = 14, k = 3
and n = 800, k = 2 
PreAlgebra [Combinations]  mysterychicken, Thursday, June 25, 2009 at 6:21pm
Nevermind I got all the answers:
1. 35 groups
2. 364 combinations
3. 319,600 choices
MC 
PreAlgebra [Combinations]  mysterychicken, Thursday, June 25, 2009 at 6:22pm
..Oops just saw that Damon. Thanks!
MC