Abox contains 20 dvds, 4 of which are defective if two dvds are selected at random (with replacement) from this box, what is the probability that both are defective?

1/25

Step-by-step explanation:

Total number of DVD's in the box = 20

Number of defective DVD's = 4

The probability of picking up a defective DVD =

This DVD is being replaced back. So this does not change the total number of DVD's in the box and the number of defective DVD's in the box.

So again the probability of picking up the second defective DVD =

The probability that both DVD's are defective will be the product of probabilities of individual events i.e.

Thus, the probability that both DVDs are defective is 1/25

step-by-step explanation:

step 1: solve one of the equations for one of the variables. let's solve the first equation for y:

step 2: substitute that equation into the other equation, and solve for x.

step 3: substitute x = 4 x = 4 x=4 into one of the original equations, and solve for y.