Need help with these-

Question

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

Answer 1

C(n,k) = n!/[ (n-k)!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

Answer 2

Nevermind I got all the answers:
1. 35 groups
2. 364 combinations
3. 319,600 choices

-MC

Answer 3

..Oops just saw that Damon. Thanks!
-MC