Question

A box in a supply room contains 21 compact fluorescent lightbulbs, of which 7 are rated 13-watt, 8 are rated 18-watt, and 6 are rated 23-watt. Suppose that three of these bulbs are randomly selected. (Round your answers to three decimal places.) (a) What is the probability that exactly two of the selected bulbs are rated 23-watt

Answer 1

The probability that exactly two of the selected bulbs are rated 23-watt is:

= 19%

Explanation:

Number of fluorescent light bulbs in the box = 21

7/21 = 13-watt rated light bulbs

8/21 = 18-watt rated light bulbs

6/21 = 23-watt rated light bulbs

The probability of selected a 23-watt rated light bulb = 6/21 = 28.57%

Size of random selection of bulbs = 3

The probability that 2 out of these 3 bulbs are 23-watt rated light bulbs is:

= 6/21 * 2/3 = 19%

b) The probability of selecting 2 of the 3 bulbs from exactly the 23-watt rated bulbs is the probability of the 23-watt rated bulbs being selected given the chance of selecting 2/3.