An Ontario company produces and ships 16 personal computers knowing that 4

of them have defective wiring. The company that purchased the computers will

thoroughly test three of the computers. The purchasing company can detect

the defective wiring.

1. What is the expected number of computers with faulty cabling? Find its

standard deviation.

2. What is the probability that the purchasing company will find exactly

three defective computers? 0.0071

3. What is the probability that the purchasing company will find two or more

defective computers? 0.1357

4. What is the probability that the purchasing company will find two or fewer

defective computers if at least one faulty computer has been purchased?

I solved 2 and 3 and justified them like it was advised but i am having a lot of trouble solving the first and fourth one