The puzzle starts by defining a "number balance". It's a balance, where you put numbers on both sides. You start on the left side by counting up from 1, and then stopping somewhere. So, in this example, we have 1, 2, 3, 4, 5 and we stop there. Keeping going, we draw the next next number (6 in this case) in the base of the balance. We call this number the "middle number" of the balance. We then keep counting on the right side, so that the balance, well, balances. In this case, 7 & 8 will work.
The Puzzle: Is this example the only possible number balance? If not, what are the others, and what is the pattern behind them?