Hi,
Eg. Say I have 10 balls. My $a_i=\frac{1}{2}$ irrespective of $i$, Then in the first take, i may take 5, second 2, 3rd 2, 4th 1. This is just a sample path. In an average i take 5 in 1st, 2( round it from $\frac{5}{2}$) in the second, 1( $\frac{3}{2}$ )in the third, 1( $\frac{2}{2}$...