1. Using Ratios to Predict Outcomes
Making Predictions
Using Ratios to Predict Outcomes

2. What is a prediction?
A prediction is a statement that describes something that is likely to happen in the future.
What are some examples of predictions you have heard people make?
What did these people base their predictions on?
When and why might you want to make a prediction?

3. Using surveys and samples
A survey is a method of collecting information. The most common types of surveys are interviews, telephone surveys, or mailed surveys.
The group being surveyed is called the population.
The entire group of
students in a school is
an example of a population.

4. To save time and money when the population is very large, part of the group, called a sample, is surveyed.
The group of students in one classroom is a sample of the population.
A good sample is:
Selected at random
Representative of the population
Large enough to provide accurate data

5. A good sample is selected at random, or without preference,
Which method would more likely produce a random sampling if surveying a large group about their favorite sport?
-Ask the first 25 students to enter the building
-Ask the first 25 students attending a basketball game

6. A good sample is representative of the population.
Which method would more likely produce a good sampling if surveying a large group about their favorite sport?
- a class of students enrolled in athletics
- A class of students enrolled in Social Studies

7. A good sample is large enough to provide accurate data
Which method would more likely produce a good sampling if surveying a large group about their favorite sport?
- A group of students in a classroom
- A group of students at a lunch table

8. Using results to predict
The responses of a good sample are proportional to the responses of the population.
So, you can use the results of a survey or past actions to predict the future results or actions of a larger group.
Writing and solving a proportion will yield a prediction.

9. Favorite Pizza Toppings
Example…
Lorenzo asked every tenth student who walked into school to name his or her favorite pizza topping.
He recorded their choices as shown in the table.
Favorite Pizza Toppings
Topping
Students
pepperoni 17
cheese 8
sausage 3
mushroom 4

10. Favorite Pizza Toppings
If there are 320 students at his school, predict how many students prefer pepperoni pizza.
Step 1: Calculate the probability that a student (from his sample) preferred pepperoni.
Favorite Pizza Toppings
Topping
Students
pepperoni 17
cheese 8
sausage 4
mushroom 3 17 32
P(pepperoni) =

11. Step 2: Write a proportion. Step 3: Solve the proportion.
Let s represent the number of students in the school ( the population) who prefer pepperoni. 17 32 s
320
Step 2: Write a proportion.
Step 3: Solve the proportion.
Since 32 time 10 equals 320,
multiply 17 by 10 to find s.
Of the 320 students, about 170 will prefer pepperoni pizza. = 17 32
170
320 =

12. Your turn !
A survey at school found that 6 out of every 10 students have access to the internet at home. If there are 250 students at the school, about how many have internet access at home?

13. Luther won 12 of the last 20 video games he played
Luther won 12 of the last 20 video games he played. Suppose he plays a total of 60 games over the next month. Predict how many of these games Luther will win.

14. Every tenth student entering the school was asked which one of the four subjects was his or her favorite.
1. Find the probability that any student attending school prefers science.

15. Every tenth student entering the school was asked which one of the four subjects was his or her favorite.
2. There are 400 students at the school. Predict how many students would prefer science.