Multiple-Probability Questions on the SAT

By Geraldine Woods, Ron Woldoff

Not surprisingly, the SAT-writers have found plenty of ways to make probability problems harder on the Math test. One of their favorite torture devices is to ask you about a probability involving multiple events.

When a problem involves multiple events, the total number of possibilities is the product of the number of possibilities for each event. If, for example, you open your closet on laundry day and find two clean shirts and three pairs of pants, the total number of outfits you can make is

2101

(assuming that you’re not a fashionista and don’t care about little things like complementary colors). This rule is known as the counting principle, although the “multiplication principle” may be a better name for it. This method works whether you’re using whole numbers, percentages, or fractions.

Multiple-probability questions on the SAT may resemble the following example.

  1. Jenny arranges interviews with three potential employers. If each employer has a 50% probability of offering her a job, what’s the probability that she gets offered all three?
    • A. 10%
    • B. 12.5%
    • C. 100%
    • D. 150%

The answer is Choice (B). Applying the counting principle to Jenny’s situation, you can say that the probability of her being offered all three jobs is

2102