Hello, Nellie!

There are: . possible samples.There are 12 resistors; 3 are defective.

If you choose 4 what is the probability that you'll get:

(a) no defective resistors . (b) 1 defective resistor . (3) 3 defective resistors

(a) "no defective" means all four are good.

There are: . ways to choose four good resistors.

Therefore: .

(b) "one defective" means 1 defective and 3 good resistors.

There are: . ways.

Therefore: .

(c) "3 defective" means all 3 defective resistors and 1 good resistor.

There are: . ways.

Therefore: .