You put two 1 dollar coins on a table, such that they touch each other (see the figure). While you fix the lower coin with your finger, you will turn the upper around it (without slipping). Somewhat later the moving coin will be back in his original position. How many rotations on his midpoint did the moving coin make?

A long and straight row of soldiers is marching with constant speed. The dog of the commander runs along the row from the end till the beginning, from the beginning till the end, from the end till the beginning etc. This takes always 2 minutes, 1 minute, 2 minutes, etc.
At some point the soldiers have to pass a very small bridge. However, the commander does not trust the strength bridge completely. He wonders how much time it will take them to pass the bridge when they stay marching with the same speed. How much time is that?

A very rich lady goes with a bag of coins (not more than 400) to the city. In the city she meets four vagabonds. She gives the first vagabond 4 coins and a quarter of the number of coins which is left in the bag. She applies the same procedure to the second, third and fourth vagabond (so division by 4 worked always). With how many coins did she leave home?