[Dave Samson]

Sherlock Holmes and Dr. Watson were travelling on the same train when they passed a field full of sheep

"Look at that solitary black sheep among all those white ones" said Watson to Holmes.

"Yes, Watson, the ratio of black sheep to white in that field is one black to three hundred and seventeen white" replied Holmes.

"But how can you be so precise" said Watson, flabbergasted.

"Elementary, my dear Watson" replied Holmes, "I counted all of the legs and divided by four!"