Now I will cut exact ly a quarter from the right of the top book and of the middle book. That will leave a quarter of the top and a quarter of the middle book. Let us call the overhang of the bottom book X, because we do not know it. The equal sign is like the table edge, and the left and the right sides of the equation have to balance. If it is exactly the half of the weight of the stack, then I am right.
Students check the numbers.
With four books, we got the overhang to be more than one book length. 2.01362 book lengths, to be exact. I can show you why these sums will be getting bigger and bigger and bigger. These sums are very famous. The infinite sum that starts this way is called harmonic series .