SOLUTION: Find the value of n in the following; 8Cn = 4 x 7Cn

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Question 1121729: Find the value of n in the following;
8Cn = 4 x 7Cn
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
use formula:

C(n,r)=n%21%2F%28r%21%28n-r%29%21%29

in your case n=8 or 7 and r=n

so you have:

8%21%2F%28n%21%288-n%29%21%29=4%2A%287%21%2F%28n%21%287-n%29%21%29%29

8%21%2F7%21=4%2A%28%28n%21%288-n%29%21%29%2F%28n%21%287-n%29%21%29%29

8=4%2A%28%288-n%29%21%29%2F%287-n%29%21%29

2=%28%288-n%29%21%29%2F%287-n%29%21%29

2=8+-+n

n=8-2

n=6

check: 8%21%2F%286%21%288-6%29%21%29=4%2A%287%21%2F%286%21%287-6%29%21%29%29 is true