mathematical beginnings logo new small.png        Crazy Clocks

possible related topics  angles, rotational symmetry, time


When you rotate this clock any multiple of 30°, the markings around the edge appear to stay in the same place. (The clock-face has rotational symmetry of order 12.) Since there is no logo in the middle of the clock-face, it is not possible to tell where the 12 o’clock position is.

The beginning picture has the minute hand past ‘half-past’ but the hour hand before ‘half-past’. This tells you that the clock must have been rotated. It is not possible to be absolutely sure of the correct time, but learners will be able to narrow it down to a few possibilities.

© Colin Foster 2012,