Given:
4/5 of the items produced are not defective
2,000 items are produced in a month
Not defective:
2,000 * 4/5 = (2,000 * 4) / 5 = 8,000 / 5 = 1,600
defective:
2,000 - 1,600 = 400
Out of the 2,000 items made in a month, only 1,600 items are not defective. The remaining 400 items are defective.