An air-conditioner manufacturer randomly samples 50 units and finds that 2 are defective. The company ships 1200 units each month.

which is the best prediction for the number of defective units in the monthly shipment?

24

25

50

48

For every 50 units they find 2 that are defective: So 1200 / 50 = 24 and 24 x 2 = 48

So out of 1200 they can predict that 48 of them will be defective.

We assume the rate of defectives in the shipment is the same as the rate of defectives in the sample. If x represents the number of defectives shipped, then that means

... 2/50 = x/1200

Multiplying by 1200 gives

... 1200·2/50 = x = 48