Each child takes 8 marbles , there are 27 marbles left over. Now let's say each child wants 10 marbles instead of 8 only. Each child takes 2 more from the 27 leftover marbles. Now there are 5 marbles left.
Number of marbles taken = 27 - 5 = 22. Since each child took 2, 22 ÷ 2 = 11. So There were 11 children. Total marbles = 10 x 11 + 5 = 110 + 5 = 115