Take out one at random first, and divide the remaining 80 into two parts and put them on both sides of the balance. If the balance is balanced on both sides, it means that the ball taken out is a slightly heavier ball; If it is unbalanced, divide the 40 balls on the heavy side into two parts and put them on both sides of the balance; Divide the 20 balls on the heavy side into two parts and put them on both sides of the balance; Divide the heavy side 10 ball into two parts and put them on both sides of the balance; Take out one of the five balls on the heavy side, divide the remaining four into two parts and put them on both sides of the balance. If the balance is balanced on both sides, it means that the ball taken out is a slightly heavier ball; If it is unbalanced, divide the two balls on the heavy side into two parts and put them on both sides of the balance. The ball on the heavy side is a slightly heavier ball.
* * * four times.