Question
A group of 15 of your friends wants to go to a concert. Unfortunately, you only have 10 tickets available to give to your friends. How many different groups of friends could you take to the concert?
Answers
combinations of 15 ten at a time
n = 15
r = 10
C(n,r) = n!/[ r!(n-r)! ]
= 15! /[ 10! (5!) ]
= 15*14*13*12*11 /(5*4*3*2)
= 15/15 * 14/2 * 13 * 12/4 * 11
= 7 * 13 * 3 * 11
= 3003
n = 15
r = 10
C(n,r) = n!/[ r!(n-r)! ]
= 15! /[ 10! (5!) ]
= 15*14*13*12*11 /(5*4*3*2)
= 15/15 * 14/2 * 13 * 12/4 * 11
= 7 * 13 * 3 * 11
= 3003
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