If 3 dice are rolled then the probability that getting different numbers or sum 16 is ____

Let A be the event that getting different numbers 
B be the event that sum is 16 and 5 be the sample space
$n\left(S\right)=6^3$
$\begin{array}{l}n\left(A\right)=6\times 5\times 4\\ n\left(B\right)=6\end{array} \begin{array}{l}B=\left\{466,646,664,556,565,655\right\}\\ A\cap B=\varphi \end{array}$
$P\left(AorB\right)=P\left(A\right)+P\left(B\right)-P\left(A\cap B\right)$
$\begin{array}{rl} & =\frac{n\left(A\right)}{n\left(S\right)}+\frac{n\left(B\right)}{n\left(S\right)}-0\\ & =\frac{6\times 5\times 4}{6^3}+\frac{6}{6^3}\\ & =\frac{21}{36}=\frac{7}{12}\end{array}$