# Math Help - binomial expansion

1. ## binomial expansion

I really dont understand how to approach this question.

the coefficient of x^2 is 3/8 in the expansion of (1+x/n)^n. find n.

any sort of help would be much appreciated.
thanks.

2. Originally Posted by wahhdoe
The binomial expansion of $\bigl(1+\tfrac xn\bigr)^n$ is
$\Bigl(1+\frac xn\Bigr)^n = 1 + {n\choose1}\Bigl(\frac xn\Bigr) + {n\choose2}\Bigl(\frac xn\Bigr)^2 + \ldots + \Bigl(\frac xn\Bigr)^n.$
You can see from that what the coefficient of $x^2$ is (in terms of n). Put it equal to 3/8 and solve for n.