Simplify m/(m+n)+n/(m+n)

$\frac{m}{m + n} + \frac{n}{m + n}$

Combine the numerators over the common denominator.

$\frac{m + n}{m + n}$

Cancel the common factor of $m + n$ .

Cancel the common factor.

$\frac{m + n}{m + n}$

Rewrite the expression.

$1$