At what precise time after 12 noon, do the two hands of a clock overlap for the first time?
Solution
The hands will cross sometime after 1 where the dashed line in diagram below indicates. To be more precise, let be the distance past 1 when this happens. We measure distances around the circular face of the clock in degrees. Then is the distance between hours and is the fraction of the hour (between 1:00 and 2:00) that the hour hand traverses to meet the minute hand. The minute hand, in the same time, meanwhile traverses the fraction of the whole clock-circle. These fractions must be equal for the hands to meet, therefore
Solving this equation gives . In other words, the hands meet one eleventh of an hour past 1. In minutes this is or 5 minutes and about 27 seconds past 1.
How many times in 12 hours do the hands meet (besides the moment at the beginning when both are vertical)? Does this suggest another approach to the problem?