Question

(Soal Tentang kombinasi) Tolong jawab soal no.23 yaa, terima lasih :D

Answer 1

3. ( n +1) / 3! ( n+1-3)! = 7/2 ( n^2+ n)
( n+1) n ( n-1) ( n-2)!/ 3! ( n-2) = 7/2 (n ^2+ n)
(n-1) / 2 = 7/2 n
n^2-n= 7n
n^2-8n=0
n ( n - 8)=0
n=8

8C5 = 8! / 5! ( 8-5)!
= 876/ 321
= 56 ( a )