Question

find n if 3.n+1 c 3=7×nc2

Answer 1

3 (n+1)C3 = 7 nC2 

3 (n+1)! / ((n-2)! 3!) = 7 (n! / ((n-2)! 2!) 

3(n-1)n! / 3! = 7 n! / 2! 

3 (n-1) = 7*6/2 

3n = 21 + 3 

n = 8