A worker takes a random sample of 290 bolts and finds that 29 of them are either too long or too short, thus making them unusable. estimate the number of unusable bolts in a production of 20,000 bolts.

You set up a proportion for these types of approximations ...

We will create a ratio of defective versus total ...

29/290=1/10 so the estimate follows ...

d/20000=1/10

d=2000

So we would estimate that about 2000 of the 20000 would be defective.