Holt CA Course 1

8-7 Making Predictions

SDAP3.2 Use data to estimate the probability of future events (e.g., batting averages or number of accidents per mile driven).Also covered: NS1.3, SDAP3.3

California Standards

Holt CA Course 1

8-7 Making Predictions

Vocabularyprediction

Holt CA Course 1

8-7 Making Predictions

A prediction is a guess about something in the future. Suppose you know the experimental probability that an airline’s flight will be on time. You can use the probability to predict how many flights out of 1,000 will be on time.

Holt CA Course 1

8-7 Making PredictionsAdditional Example 1: Using Experimental

Probability to Make PredictionsA store claims that 78% of shoppers end up buying something. Out of 1,000 shoppers, how many would you predict will buy something?

You can write a proportion. Remember that percent means “per hundred.”

Holt CA Course 1

8-7 Making PredictionsAdditional Example 1 Continued

100x 100 ____ 78,000

100 ______= Divide both sides by 100.

x = 780You can predict that about 780 out of 1,000 customers will buy something.

Think: 78 out of 100 is how many out of 1,000?

100 • x = 78 • 1,000100x = 78,000

The cross products are equal.

78100___ x

1,000=

Holt CA Course 1

8-7 Making PredictionsCheck It Out! Example 1

A store claims 62% of shoppers end up buying something. Out of 1,000 shoppers, how many would you predict will buy something?

You can write a proportion. Remember that percent means “per hundred.”

Holt CA Course 1

8-7 Making PredictionsCheck It Out! Example 1 Continued

100x 100 ____ 62,000

100 ______= Divide both sides by 100.

x = 620You can predict that about 620 out of 1,000 customers will buy something.

Think: 62 out of 100 is how many out of 1,000?

100 • x = 62 • 1,000

100x = 62,000

The cross products are equal.

62100___ x

1,000=

Holt CA Course 1

8-7 Making PredictionsAdditional Example 2: Using Theoretical Probability to Make

Predictions If you roll a number cube 30 times, how many times do you expect to roll a number greater than 2?

2 3 __ x

30 ___= Think: 2 out of 3 is how many

out of 30?3 • x = 2 • 30

3x = 60The cross products are equal.

P(greater than 2) = = 46__ 2

3__

Divide both sides by 3.

x = 20

3x 3 __ 60

3 __=

Holt CA Course 1

8-7 Making PredictionsAdditional Example 2 Continued

You can expect to roll a number greater than 2 about 20 times.

If you roll a number cube 30 times, how many times do you expect to roll a number greater than 2?

Holt CA Course 1

8-7 Making PredictionsCheck It Out! Example 2

If you roll a number cube 30 times, how many times do you expect to roll a number greater than 3?

1 2 __ x

30 ___= Think: 1 out of 2 is how many

out of 30?2 • x = 1 • 30

2x = 30The cross products are equal.

x is multiplied by 2.

P(greater than 3) = = 36__ 1

2__

Divide both sides by 2.

x = 15

2x 2 __ 30

2 __=

Holt CA Course 1

8-7 Making PredictionsCheck It Out! Example 2 Continued

You can expect to roll a number greater than 3 about 15 times.

If you roll a number cube 30 times, how many times do you expect to roll a number greater than 3?

Holt CA Course 1

8-7 Making Predictions Additional Example 3: Problem Solving Application

Suppose the managers of a second stadium, like the one on page 411, also sell yearly parking passes.The managers of the second stadium estimate that the probability of a person with a pass attending any one event is 50%. The parking lot has 400 spaces. If the managers want the lot to be full at every event, how many passes should they sell?

Holt CA Course 1

8-7 Making Predictions11 Understand the Problem

The answer will be the number of parking passes they should sell.List the important information:• P(person with pass attends event): = 50%• There are 400 parking spaces

The managers want to fill all 400 spaces. But on average, only 50% of parking pass holders will attend. So 50% of pass holders must equal 400. You can write an equation to find this number.

22 Make a Plan

Holt CA Course 1

8-7 Making PredictionsSolve33

50100___ 400

x____= Think: 50 out of 100 is 400

out of how many?

100 • 400 = 50 • x40,000 = 50x

The cross products are equal.

40,000 50 ______ 50x

50 ___ = Divide both sides by 50.

800 = x

The managers should sell 800 parking passes.

Holt CA Course 1

8-7 Making Predictions

If the managers sold only 400 passes, the parking lot would not usually be full because only about 50% of the people with passes will attend any one event. The managers should sell more than 400 passes, so 800 is a reasonable answer.

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Holt CA Course 1

8-7 Making PredictionsCheck It Out! Example 3

The concert hall managers sell annual memberships. If you have an annual membership, you can attend any event during that year.The manager estimates that the probability of a person with a membership attending any one event is 60%. The concert hall has 600 seats. If the manager want the seats to be full at every event, how many memberships should she sell?

Holt CA Course 1

8-7 Making Predictions11 Understand the Problem

The answer will be the number of memberships they should sell.List the important information:• P(person with membership attends event): = 60%• There are 600 seats

The manager wants to fill all 600 seats. But on average, only 60% of membership holders will attend. So 60% of membership holders must equal 600. You can write an equation to find this number.

22 Make a Plan

Holt CA Course 1

8-7 Making PredictionsSolve33

60100___ 600

x____= Think: 60 out of 100 is 600

out of how many?

100 • 600 = 60 • x60,000 = 60x

The cross products are equal.

60,000 60 ______ 60x

60 ___ = Divide both sides by 60.

1,000 = x

The manager should sell 1,000 annual memberships.

Holt CA Course 1

8-7 Making Predictions

If the manager sold only 600 annual memberships, the seats would not usually be full because only about 60% of the people with memberships will attend any one event. The managers should sell more than 600 passes, so 1,000 is a reasonable answer.

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