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

3

step-by-step explanation:

in standard form:

a= dictionaries

b= maps

you have to buy 3 dictionaries, so put a 3 next to the a (dictionaries) so that you can multiply them by each other.

a3+b= 60 (the amount of money you have)

we already know the cost of a=15 so replace a with $15

($15 x 3)+b=60

multiply 15 and 3 to get $45 and replace it with $45

45+b=60

and then replace b with 15 to get the total:

45+15=60

that means you have $15 left after buying 3 dictionaries.

15 divided by the cost of a map ($5) equals 3.

so you can buy 3 maps.

sorry if it was confusing!

i dont know men

step-by-step explanation: