Example #2: Counting in binary

When you reach puzzle 21, binary numbers are introduced into the puzzles. In the following picture, a number is represented by four bits. To read the number from the bits, all you have to know is that the top bit is worth 1, the second bit down is worth 2, the third bit is worth 4, and the fourth bit is worth 8. Simply add together the values of the bits that are pointed right. For example,