There are 8 identical balls. In that one of the ball is overweight.
There are only two chances to weigh in the weighing machine. How to find the overweight ball?
First weigh 3 against 3 balls. If the ball contains among these six balls, then take the three balls which weighed over, and weigh the ball 1 against 1.
If the balls are not equal and any one of the ball weighs more, that is the overweight ball, else the one among the three which is not weighed is the ball.
If the 3 against 3 balls were equal, then weigh the 2 balls, then the overweight ball will be found.