Education.com
Try
Brainzy
Try
Plus

# Averages, Probability, and Combinations for CBEST Exam Study Guide (page 4)

By
Updated on Mar 29, 2011

### Probability

Suppose you put one entry into a drawing that had 700 entrants. What would be your chances of winning? They would be 1 in 700 of course. Suppose you put in two entries. Your chances would then be 2 in 700, or reduced, 1 in 350. Probabilities are fairly simple if you remember the few tricks that are explained in this section.

#### Sample Probability Question

1. If a nickel were flipped thirteen times, what is the probability that heads would come up the thirteenth time?
1. 1:3
2. 1:2
3. 1:9
4. 1:27
5. 1:8

Use the four Success Steps to solve the problem.

1. Form a fraction.
2. Each time a coin is flipped, there are two possibilities— heads or tails—so the number 2 goes on the bottom of the fraction. The thirteenth time, there are still going to be only two possibilities.
3. The number of possibilities that make the event (heads) true is 1. There is only one head on a coin. Therefore, the fraction is . "Thirteen times" is extra information and does not have a bearing on this case.
4. The answer is choice b, 1:2. The numerator goes to the left of the colon and the denominator to the right.

#### Sample Probability Question

1. A spinner is divided into six equal parts. The parts are numbered 1–6.When a player spins the spinner, what are the chances the player will spin a number less than 3?

Once again, use the four Success Steps.

1. Form a fraction.
2. Total number of possibilities = 6. Therefore, 6 goes on the bottom.
3. Two goes on top, since there are two numbers that are less than 3: 1 and 2.
4. The answer is , or reduced , = 1:3.