10-4 Theoretical Probability

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10-4 Theoretical Probability

I can find the theoretical probability of an event.

1. Two coins are tossed. What is the probability of getting two heads?

2. Give the probability that the roll of a number cube will show 1 or 4.

3. Give the expected number of rolls that will result in a 2 if a number cube is rolled 42 times.

14

13

7

10-4 Theoretical Probability

Problem of the Day

The name of a U.S. state is spelled out with letter tiles. Then the tiles are placed in a bag, and one is picked at random. What state was spelled out if the probability of picking the letter O is

Ohio; Colorado; Oregon

12 ?

38 ? 1

3 ?

10-4 Theoretical Probability

I can find the theoretical probability of an event.

10-4 Theoretical Probability

Vocabulary

theoretical probabilityequally likelyfair

10-4 Theoretical Probability

Theoretical probability is used to find the probability of an event when all the outcomes are equally likely.

Equally likely outcomes have the same probability.

If each possible outcome of an experiment is equally likely, then the experiment is said to be fair. Experiments involving number cubes and coins are usually assumed to be fair.

10-4 Theoretical Probability

Additional Example 1A: Finding Theoretical Probability

Andy has 20 marbles in a bag. Of these, 9 are clear and 11 are blue. Find the probability of drawing a clear marble from the bag? Write your answer as a fraction, as a decimal, and as a percent.

P = number of ways the event can occur total number of equally likely outcomes

P(clear) = number of clear marblestotal number of marbles

= 0.45 = 45%

920

Write the ratio.

Substitute.

Write as a decimal and write as a percent.

= 920

The theoretical probability of drawing a clear marble is , 0.45, or 45%.

10-4 Theoretical Probability

Find the probability of drawing a blue marble from the bag.

Additional Example 1B: Finding Theoretical Probability

P = number of ways the event can occur total number of equally likely outcomes

P(blue) = number of blue marblestotal number of marbles

= 1120

= 0.55 = 55%

The theoretical probability of drawing a clear marble is , 0.55, or 55%.1120

Write the ratio.

Substitute.

Write as a decimal and write as a percent.

10-4 Theoretical Probability

P = number of ways the event can occur total number of equally likely outcomes

P(green) = number of green marblestotal number of marbles

= 0.4 = 40%

The theoretical probability of drawing a green marble is , 0.4, or 40%.820

Write the ratio.

Substitute.

Write as a decimal and write as a percent.

Check It Out: Example 1A

Jane has 20 marbles in a bag. Of these 8 are green.Find the probability of drawing a green marble from the bag? Write your answer as a fraction, as a decimal, and as a percent.

= 820

10-4 Theoretical Probability

Find the probability of rolling a number more than 4 on a fair number cube.

P = number of ways the event can occur total number of equally likely outcomes

P(number more than 4) = 2 numbers more than 4 6 possible outcomes

= 26

= 13

0.33 33%The theoretical probability of rolling a number more than 4 is 0.33, or 33%. 13 ,

Check It Out: Example 1B

For a fair number cube, each of the six possible outcomes is equally likely. There are 2 ways to roll a number greater than 4: 5 or 6.

10-4 Theoretical Probability

Additional Example 2A: School Application

There are 13 boys and 10 girls on the track team. The name of each of the team members is written on an index card. A card is drawn at random to choose a student to run a sprint and the card is replaced in the stack.

Find the theoretical probability of drawing a boy’s name.

P(boy)= 1323

Substitute.

P(boy) = number of boys on the team number of members on the team

10-4 Theoretical Probability

The sum of the probabilities of an event and its complement is 1.

Remember!

10-4 Theoretical Probability

Additional Example 2B: School Application

Find the theoretical probability of drawing a girl’s name.

+ P(girl) = 11323

P(boy) + P(girl) = 1

There are 13 boys and 10 girls on the track team. The name of each of the team members is written on an index card. A card is drawn at random to choose a student to run a sprint and the card is replaced in the stack.

Substitute for P(boy). 1323

Subtract from both sides 1323

- = -1323

1323

P(girl) = 1023 Simplify.

10-4 Theoretical Probability

Check It Out: Example 2A

A teacher has written the name of each student on a piece of paper and placed the names in a box. She randomly draws a paper from the box to determine which student will present the answer to the problem of the day.

If there are 15 boys and 12 girls in the class, what is the theoretical probability that a girl’s name will be drawn?

=1227

Find the theoretical probability.

Substitute.

P(girl) = number of girls in the classnumber of students in the class

10-4 Theoretical Probability

Check It Out: Example 2B

What is the theoretical probability that a boy’s name will be drawn?

+ P(boy) = 11227

P(girl) + P(boy) = 1

Substitute for P(girl). 1227

Subtract from both sides 1227

- = -1227

1227

P(boy) = 1527 Simplify.

10-4 Theoretical Probability

Standard Lesson Quiz

Lesson Quizzes

Lesson Quiz for Student Response Systems

10-4 Theoretical Probability

Lesson QuizFind the probabilities. Write your answer as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent. You have 11 cards, each with one of the letters from the word mathematics.

1. Find the probability of drawing an m from the pile of shuffled cards.

2. Find the probability of drawing a vowel. 3. Find the probability of drawing a consonant. 7

11

211

4 11

, 0.18, 18%

, 0.36, 36%

, 0.64, 64%

10-4 Theoretical Probability

1. A number cube is rolled. Identify the probability of getting a number less than 4 as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent.

A.

B.

C.

D.

Lesson Quiz for Student Response Systems

10-4 Theoretical Probability

2. There are 40 balls in a bag. Of these 8 are white, 7 are blue, 12 are green, and 13 are yellow. Identify the probability of drawing a white ball as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent.

A.

B.

C.

D.

Lesson Quiz for Student Response Systems