Question

On the playground, children are made to stand for drill either 30 in a row or 20 in a row, all rows are complete and no child is left out. What is the lowest possible number of children in that school?

Answer 1

30 times table :30, 60, 90, 120, 150, 180, 210, .....

20 times table :20, 40, 60,80, 100....

From the above table, we can see that 60 is the lowest common multiple of 30 and 20.

Therefore, the least possible strength of the school is 60.