7th Grade Math

Lesson 3A Predictions 459

Experimental Probability

When two number cubes are rolled together 75 times, a sum

of 9 is rolled 10 times. What is the experimental probability of

rolling a sum of 9?

P(9) = ___number of times a sum of 9 occurs

total number of rolls

= _^10

75

or _^2

15

The experimental probability of rolling a sum of 9 is _^2

15

.

a. In the above experiment, what is the experimental probability

of rolling a sum that is not 9?

Experimental and Theoretical

Probability

The graph shows the results of an experiment in which a spinner

with 3 equal sections is spun sixty times. Find the experimental

probability of spinning red for this experiment.

The graph indicates that the

spinner landed on red 24 times,

blue 15 times, and green 21 times.

P(red) = ___number of times red occurs

total number of spins

= _^24

60

or _^2

5

The experimental probability

of spinning red is _^2

5

.

Compare the experimental probability you found in Example 2

to its theoretical probability.

The spinner has three equal sections: red, blue, and green. So,

the theoretical probability of spinning red is _^1

3

. Since ^2
5
≈ ^1
3
, the
experimental probability is close to the theoretical probability.

b. Refer to Example 2. If the spinner was spun 3 more times and

landed on green each time, find the experimental probability of

spinning green for this experiment.

c. Compare the experimental probability you found in Exercise b

to its theoretical probability.

Trials Trials A trial is one

experiment in a series of

successive experiments.

Spinner Results

Color

Number of Times

Green

Blue

Red

0 102030

21

15

24

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