Boys and Bikes

When hundreds of High School boys attended a Walt Disney film at one of the local theatres, hundreds of bicycles were parked on a vacant city lot.

When the picture was over, the rush started. The hundreds of boys descended on the hundreds of bikes, sorted themselves out in a few moments, and pedalled away, each on his own machine.

A school boy might not always know that the opposite angles of a cyclic quadrilateral are supplementary, but he sure knows which is his own bike.