Question

Twelve of the 100 digital video recorders (DVRs) in an inventory are known to be defective. What is the probability you randomly select a DVR that is not defective?

Answer 1

There are 100 DVRs in the inventory, and 12 of them are defective. Therefore, the number of non-defective DVRs is:

100 - 12 = 88

The probability of selecting a non-defective DVR can be found by dividing the number of non-defective DVRs by the total number of DVRs:

P(non-defective DVR) = number of non-defective DVRs / total number of DVRs

= 88 / 100

= 0.88

Therefore, the probability of randomly selecting a DVR that is not defective is 0.88, or 88%.

Answer 2

Explanation:

a probability is always the ratio

"desired" cases / totally possible cases

the totally possible cases here are 100.

now, the question focuses on non-defective units.

how many out of the 100 are non-defective ?

well, 100 - 12 = 88 units.

so, the probability to select a non-defective (= working) unit is

88/100 = 22/25 = 0.88

in other words, as a mean and expected value, in 88 of 100 attempts, or in 22 of 25 attempts you will select a non-defective unit.