As a manager at an electronics retail store you receive a sh

As a manager at an electronics retail store, you receive a shipment of 28 iphones, 4 of which are defective.

If 6 are sold at random, find the probability that none of the ones sold are defective.

What is the probability of at least 1 of the six being defective?

Solution

Of the 28 I phones, 4 are defective and 24 are not defective.

The probability that the 1st selection will not be defective is   24/28   

The probability that the 2nd selection will not be defective is 23/27

The probability that the 3rd selection will not be defective is 22/26  

The probability that the 4th selection will not be defective is   21/25

The probability that the 5th selection will not be defective is 20/24

The probability that the 4th selection will not be defective is 19/23

The probability that none of the 6 iphones are defective is (24/28)*(23/27)*(22/26)*(21/25)*(20/24)*(19/23)

= 96909120/271252800 = 0.357265 ( approx.)

The probability that at least 1 of the 6 iphones is defective is 1 – 0.357265 = 0.642735 ( approx.)