4. A box contains 8 red, 3 white and 9 blue balls. Three balls are to be drawn without replacement. What is the probability that more blues than whites are drawn? (42)

Hint: Present this event as a union of simpler events (use “B” (for blue), “W” and “R” letters. Do not forget that BRR, for example, also satisfies the requirement.

5. A production lot has has 100 units of which 25 are known to be defective. A random sample of 4 units is chosen without replacement. What is the probability that the sample will contain no more than 2 defective units.

Hint: (a) Notice that “At most 2 defective” = “0 defective” + “1 defective” + “2 defective”.

(b) Notice that the number of outcomes corresponding to “0 defective” is N(0)=C75,4 (meaning that all four units are taken out of 75 non-defective). Using the same approach, find N(1) and N(2). Notice that they are described as intersections (“and”) of two events each.

(c) Add together the numbers of outcomes corresponding to all three events in the right-hand side, and divide by the total number of possible selections (4 out of 100).

Practice with the Problems 1.6-1.7, 1.12,1.26, 1.30-1.32, 1.39-1.42, 1.49-1.51, 1.81-1.89, 1.93-1.95

From Shaum’s outlines.

During the test you can use my Lecture files (PPT printouts) and Mathematica. No other materials are allowed