In detail

The coin that rolls

The coin that rolls

We have two identical coins on one table next to each other. If we turn the coin on the left, without lifting it from the table, rolling it over the edge of the coin on the right until it is placed in the area marked in red,

How will the coin be oriented? The 1 will it be straight or upside down?

Solution

Although intuitively it seems that the coin should turn around as we spin it around the middle of the circumference of the other coin, it will actually take a full turn so that it will be in the same orientation as at the beginning, with the 1 to the right.