Hannah was sitting in front of a clock. When she observed it for the first time, the hour hand was at a minute mark and the minute hand was six minutes ahead. After some time, she observed the clock again to find that the hour hand was exactly on a different minute mark and the minute hand was seven minutes ahead of its time.
wikipedia.org Zagadki Zagadka logiczna Diofantosa z III wieku - tylko najtęższe umysły są w stanie ...