A box contains 8 light bulbs, two of which do not work.

Question

If two bulbs are selected, the probability of selecting both bulbs that do not work is

a. 1/4

b. 3/4

c. 1/28

d. 11/28

Answer 1

 

A box contains 8 bulbs (In which 6 working , 2 are not working) .

Selecting two bulbs .

Total number of possible choices = Number of ways in which the two bulbs can be select from the total of 8 bulbs .

n = 8C₂

n = (8*7)/(2*1) = 28

Number of favorable choices = The number of ways in which 2 defected bulbs selected out of 2 defected bulbs .

= 2C₂ = 1

Probability of selecting two defected bulbs = (Number of favorable choices)/(Total number of possible choices)

                                                       = 1/28 

Therefore Probability of selecting two defected bulbs is 1/28 .

Option (c) is the correct answer.