Problem 23

$$\begin{array}{lcl} 23.John\:has\:exactly\:7\:blue\:trousers,\:5\:brown\:trousers\:and\\ 3\:black\:trousers\:in\:his\:chest\:of\:drawers. \:If\:he\:picks\:up\\ one\:pair\:of\:random\:trousers\:from\:his\:chest\:of\:drawers,\:\\ what\:is\:the\:probability\:that\:the\:trousers\:are\:either\:blue\\ or\:black\:?\\ \\ \end{array}$$