LESSON 2: Proportional Relationships

Which is the better buy?

Value-Mart is advertising a Back-to-School sale on pencils. A pack of 30 sells for $7.97 whereas a 12-pack of the same brand cost $4.77. Which is the better buy? How do you know?

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LESSON 2: Proportional Relationships

How much am I paying for this, anyway? Is there a “better buy” at the stores?

Two new self-service ice cream stores opened this summer. At both stores, Ice Cream Emporium and Ice Cream Treats, ice cream is sold by the weight.

Ice Cream Emporium (Store A) Weight (ozs) Cost ($) 3 1.20

6 2.40

10 4.00

15 6.00

Ice Cream Treats (Store B) Weight (ozs) Cost ($) 3 1.20

6 2.10

10 3.00

15 4.50

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LESSON 2: Proportional Relationships What did we learn from the ice cream store example?

At Store A, describe what people pay for the ice cream they purchase.

How much will 8 ounces of ice cream cost? At Store B, describe what people pay for the ice cream they purchase.

How much will 8 ounces of ice cream cost? Dr. Basta 3

LESSON 2: Proportional Relationships

X (weight in ozs) 12.5

Y (cost in $) 5

Using variables and equations: y = kx

12.5

5 ÷ 12.5 = 0.4

12.5 × 0.4 = 5

5 Multiplication and division are related operations.

k = 0.4

Only at Store A can we say that “cost is proportional to weight”. Even “0 ounces” can be multiplied by $0.40 to find that the cost of 0 ounces is $0. There is a constant, k, which can be used to find the cost of every ice cream ordered.

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LESSON 2: Proportional Relationships

During Jose’s physical education class today, students visited activity stations. Next to each station was a chart depicting how many Calories (on average) would be burned by completing the activity. Is the number of Calories burned proportional to time? How do you know? If Jose jumped rope for 6.5 minutes, how many calories would he expect to burn?

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LESSON 2: Proportional Relationships Alex spent the summer helping out at his family’s business. He was hoping to earn enough money to buy a new $220 gaming system by the end of the summer. Halfway through the summer, after working for 4 weeks, he had earned $112. Alex wonders, “If I continue to work and earn money at this rate, will I have enough money to buy the gaming system by the end of the summer?” To check his assumption, he decided to make a table. He entered his total money earned at the end of week 1 and his total money earned at the end of Week 4.

Week Total Earnings 0 1

$28

2 3 4

$112

5 6 7 8

Are Alex’s total earning proportional to the number of weeks he worked? How do you know? Dr. Basta 6

Problem Set: Module 1, Topic A, Lesson 2 [1] Ms. Albero decided to make juice to serve along with the pizza at the Student Government party. The directions said to mix 2 scoops of powdered drink mix with a half a gallon of water to make each pitcher of juice. One of Ms. Albero’s students said she will mix 8 scoops with 2 gallons of water to get 4 pitchers. How can you use the concept of proportion to decide whether the student is correct? [2] John is filling a bathtub that is 18 inches deep. He notices that it takes two minutes to fill the tub with three inches of water. He estimates it will take ten more minutes for the water to reach the top of the tub if it continues at the same rate. Is he correct? Explain.

Student Name: ____________________________ Dr. Basta 7