A supermarket claims that their checkout scanners correctly price 99.8% of the items sold. How many items would you expect to buy, on average, to find one that scans incorrectly?
A) 200
B) 998
C) 99.8
D) 2
E) 500

Question

Quizplus · Accepted Answer

To find the average number of items you need to buy to get one that scans incorrectly, you take the inverse of the error rate. The error rate is 0.2% (100% - 99.8%), which is 0.002 when expressed as a decimal. The inverse of 0.002 is 1/0.002 = 500.

A Supermarket Claims That Their Checkout Scanners Correctly Price 99