A school clock is showing the wrong time, but the teacher says, "It's wrong now, but it is right 11 times a...

arithmetic/clock/swapped.hands New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

A school clock is showing the wrong time, but the teacher says, "It's
wrong now, but it is right 11 times a day."  How can that be?

Show solution

The minute and hour hands have been reversed [Editor: the original has no comma here], so the clock shows the
correct time [Editor: "time" is not in the original] when the hour and minute hands are aligned.  This happens
11 times in a 12 hour period.  I usually think of a day as being
24 hours so I would say the clock is correct 22 times a day.

-- Glenn C. Rhoads (rhoads@paul.rutgers.edu)

[ Editor: see also the entries "overlap" and "reversible". ]