Hi,
"7% of al switches produced are defective. if 200 switches are selected at random,
what us the probability that more than 20 will be defective?"
BINOMIAL Distribution P(x) = nCx* 
where p and q are the probabilities of success and failure respectively.
In this case p = .07 & q = .93 & n = 200 nCx = 
P(20) =(200C20)(.07)^20(.93)^180 Or binompdf(200, .07, 20)on calculator
Recommend using Your TI calculator for cumulative probabilities
and/or stattrek.com as an excellent reference.
P(x>20) = 1 - P(x ≤ 20) = 1 - binomcdf(200, .07, 20) on a Ti calculator
Without a Calculator: 1 - [ P(0) + P(1) + P(2) .... + P(20)]
Tedious, but can be done.
Again: stattrek.com is an excellent reference (also has calculators)
