Given 80 balls, outwardly identical, but one of them is slightly lighter than the others.

Given 80 balls, outwardly identical, but one of them is slightly lighter than the others. Using a beam balance, select a light ball in 4 weighings.

1) We have 80 balls in total. We take half of them and weigh them on a scale so that there are 20 balls on each scale.

If one of the scales is higher, then there is a light ball. We select these 20 balls.

2) During the second weighing out of 20 balls, select half and weigh so that there are 5 balls on each of the scales.

If one of the scales is higher, then there is a light ball. We select these 5 balls.

3) During the third weighing, divide 5 balls by 2 and 2 for weighing. Choosing the lighter ones. If the scales show the same, the ball we need is the last remaining one.

4) In the fourth weighing on the scales, we leave 1 ball out of the two selected and determine which one is easier.

Answer: We carry out weighing in the same way as described above, choosing lighter or remaining balls on the scales.