The times at which the hands on a clock face cross (hour and minute hand) is given by:
t = (60/11)h, where: h is the time past midday in hours, an integer value and 0≤h, i.e. at midday h=0.
If you wish to know how I derived this, just ask.
(This was a question posed to us by my physics teacher, "At midday, the hands of the clock are directly over each other, at what other times does this also occur?")