# Lesson 17

The Stock Market

## 17.1: Revisiting Interest and Depreciation (5 minutes)

### Warm-up

The warm-up reminds students of their understanding of percentage increase and decrease in preparation for the shares questions later in the lesson. Some students will use different strategies; identify those for the discussion after the activity.

### Launch

Remind students that they can use any strategies from sixth grade for answering the percentages questions.

### Student Facing

- Lin deposited $300 in a savings account that has a 2% interest rate per year. How much is in her account after 1 year? After 2 years?
- Diego wants to sell his bicycle. It cost $150 when he bought it but has depreciated by 15%. How much should he sell it for?

### Student Response

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### Anticipated Misconceptions

If students forget about using an equation to calculate percent increase or decrease, remind them that they can use the equation \(y=kx\) to figure out the answers to the questions.

### Activity Synthesis

The most important thing is to recall efficient methods of calculating percent increase and decrease, such as setting up an equation in the form A% of B is C. Select students to share their methods in preparation for the next activity.

## 17.2: Gains and Losses (10 minutes)

### Activity

Students are introduced to the idea of the stock market and how the value changes. They apply their understanding of negative numbers to percentage change as well as money (MP4).

### Launch

Introduce the concept of shares in a company. They have a specific value at a specific time that can change up or down. They represent a measure of the worth of the company. We sometimes express the change as a value in dollars, so investors can see how much money they will make or lose. We can also present these as a percentage to compare companies in terms of growth.

Before students begin working on the task consider asking how they would represent an increase or decrease in value so that it was easily apparent.

To familiarize students with the information in the table, consider asking which companies’ stocks increased in value and which companies’ stocks decreased in value from day 1 to day 2. Have students explain their reasoning and come to an agreement before anyone begins doing calculations.

*Representation: Internalize Comprehension.*Activate or supply background knowledge. Allow students to use calculators to ensure inclusive participation in the activity.

*Supports accessibility for: Memory; Conceptual processing*

*Writing, Conversing: MLR5 Co-craft Questions.*Without revealing the questions that follow, display the table from the print statement for all to see. Give students 1–2 minutes to interpret the table, and write down possible mathematical questions that could be asked about the situation. Invite students to compare their questions with a partner before selecting 2–3 to share with the class. This will draw students' attention to the relationships between the four quantities in this task, and provide an opportunity for them to produce the language of mathematical questions.

*Design Principle(s): Cultivate conversation*

### Student Facing

- Here is some information from the stock market in September 2016. Complete the table.
company value on day 1 (dollars) value on day 2 (dollars) change in value (dollars) change in value as a percentage of day 1 value Mobile Tech Company 107.95 111.77 3.82 3.54% Electrical Appliance Company 114.03 2.43 2.18% Oil Corporation 26.14 25.14 -3.83% Department Store Company 7.38 7.17 Jewelry Company 70.30 2.27% - Which company's change in dollars had the largest magnitude?
- Which company's change in percentage had the largest magnitude?

### Student Response

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### Activity Synthesis

The important part of this activity is that students use a directed quantity for percentage change to model decrease in value as negative and increase as positive. Ask students how they would prefer the information to be presented, and ask them to support their conclusions.

## 17.3: What is a Stock Portfolio? (15 minutes)

### Activity

This task introduces the concept of a stock portfolio being a selection of stocks an investor might own to try to make money—students examine the change in portfolio and evaluate the value. They must use both positive and negative change, and percentage change.

### Launch

Introduce the concept of a portfolio of shares in a company.

*Engagement: Develop Effort and Persistence.*Encourage and support opportunities for peer interactions. Invite students to talk about their ideas with a partner before writing them down. Display sentence frames to support students when they explain their strategy. For example, “In order to calculate the total value, first I ___ because…” or “The portfolio increased/decreased because….”

*Supports accessibility for: Language; Social-emotional skills*

*Representing, Listening: MLR8 Discussion Supports.*Demonstrate how to complete the first row of the second table about Technology Company’s total value, as you think aloud. Students can listen to your mathematical language and reasoning as you describe what the price change represents and find the new price, then calculate the total value. This will help invite more student participation, conversations, and meta-awareness of language involving representing financial situations of the stock market with positive and negative change and percentage change.

*Design Principle(s): Support sense-making; Maximize meta-awareness*

### Student Facing

A person who wants to make money by investing in the stock market usually buys a portfolio, or a collection of different stocks. That way, if one of the stocks decreases in value, they won’t lose all of their money at once.

- Here is an example of someone’s stock portfolio. Complete the table to show the total value of each investment.
name price (dollars) number of shares total value (dollars) Technology Company 107.75 98 Airline Company 133.54 27 Film Company 95.95 135 Sports Clothing Company 58.96 100 - Here is the same portfolio the next year. Complete the table to show the new total value of each investment.
company old price (dollars) price change new price (dollars) number of shares total value (dollars) Technology Company 107.75 +2.43% 98 Airline Company 133.54 -7.67% 27 Film Company 95.95 87.58 135 Sports Clothing Company 58.96 -5.56% 100 - Did the entire portfolio increase or decrease in value over the year?

### Student Response

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### Activity Synthesis

The important part of this activity is that it extends on the context previously examined, ahead of students building their own portfolio in a later activity.

## 17.4: Your Own Stock Portfolio (15 minutes)

### Activity

Distribute copies of the "Stocks Prices"

Students calculate their own portfolio

Distribute copies of the "Changes in Stock Prices after 3 Months" so they can calculate the change.

### Launch

Distribute copies of the Stock Prices Blackline Master. Have prepared the Changes in Stock Prices after 3 Months Blackline Master.

*Action and Expression: Internalize Executive Functions.*To support development of organizational skills, check in with students within the first 2-3 minutes of work time. Check to make sure students show calculations for the total value of their portfolio as to not go over $100.

*Supports accessibility for: Memory; Organization*

### Student Facing

Your teacher will give you a list of stocks.

- Select a combination of stocks with a total value close to, but no more than, $100.
- Using the new list, how did the total value of your selected stocks change?

### Student Response

### Activity Synthesis

Have students trade with a partner and check each other's work. (Answers vary because each student worked with a different selection of stocks.)

Have students examine the "Changes in Stock Prices after 3 Months" page and discuss:

- How can you tell if the price of a stock increased or decreased from looking at this list?
- Which company's stock price increased or decreased by the most?
- Without doing any calculations, predict which company's stock price had the largest increase as a percentage of its starting value.
- Without doing any calculations, predict which company's stock price had the largest decrease as a percentage of its starting value.

*Writing, Speaking: MLR1 Stronger and Clearer Each Time.*Use this routine to give students a structured opportunity to revise and refine their initial response to: “Using the new list, how did the total value of your selected stock change?”. Ask students to meet with 2–3 other partners in a row for feedback. Provide students with prompts for feedback that will help pairs strengthen their ideas and clarify their language (e.g., “What is a quantity that changed?”, and “What other details are important?”, etc.). Students can borrow ideas and language from each partner to strengthen their final response.

*Design Principle(s): Optimize output (for description)*

## Lesson Synthesis

### Lesson Synthesis

Key learning points:

- There are a number of contexts in which using negative numbers to represent directed change is important; the stock market is one of them.
- Percentage change down can be represented with a negative percentage

Discussion questions:

- Which way of showing the change do you prefer, percentage or monetary value?
- Can you think of other situations in life where using a negative to represent a change would be useful?