To find the probability that the restaurant buys at least 2 non-defective units, we find the probability that they purchase either 2 or 3 non-defective units:
They purchase <u>3 units total</u>, so this is <u>n</u>. We want the <u>probability of either 2 or 3</u> non-defective units; this means <u>r is 2 and r is 3</u>. In this case we want the probability that the units are non-defective. Since there are 4 defective units, this means there are 12-4=8 non-defective units; this makes the <u>probability of a non-defective unit 8/12 = 2/3. This is p</u>.