Question

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

Answer 1

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.

Answer 2

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