Question

A shelf in the metro department store contains 85 colored ink cartridges for a popular ink jet printer, seven of the cartridges are defective.

A: If a customer selects 2 at random, what is the probabilty they are both defective?

B: If a customer selects 2 at random, what is the probability that at least 1 is defective?

Answer 1

Let x be number of defective cartridges.

There are total 85  cartridges , 7 are defectives so 78 are non defectives.

A) P( x = 2 )

= ( Number of ways getting 2 defective cartridges out of 7 defective cartridges ) /( Number of ways selecting 2 cartridges out of total 85 cartridges )

= =  

= 0.0059

B) P( at least 1 defective ) = 1 - P( no defectives )

= 1 - P( x = 0 )

= 1 -  

= 1-

= 1 - 0.8412

= 0.1588