exam review HELP!!!

The question is:

Mr. Brown recently purchased 100 randomly selected machine scres with a defective rate of 10%. What is the probability that he finds 12 or more defective screws in his selection?

I have one answer, my class mate has another and yet a member of another class has a third!

What formula should be used? I chose (mu) = np (sigma) = square root of np (1-p)

Thanks for any input!