In this activity, students are introduced to the idea of the stock market and how the values of shares in a stock can change daily. They apply their understanding of negative numbers to percentage changes and money. 

The purpose of this discussion is for students to share their responses and reasoning and to share strategies for calculating percent increase or decrease. Begin by inviting students to share their responses and reasoning for completing the rows for the electrical appliance company and the oil corporation. Poll the class to see which students used or did not use the percentage change to determine the unknown value.

Then invite students to share their responses and reasoning for determining the unknown values in the last two rows of the table. 

In this activity, students are introduced to the concept of a stock portfolio. They calculate the value of a given number of shares in a company, the new value of the shares after a change in price, and the total value of a given portfolio. Students see both positive and negative values for both absolute and percent change.

The purpose of this discussion is to continue to build students' understanding of the context of investing in shares of stocks, in preparation for students to build their own stock portfolio in the next activity. Begin by inviting students to share their responses and reasoning for whether the value of the given portfolio increased or decreased. Record their thinking for all to see. If necessary, consider discussing the following questions:

• "How did you determine the new price of one share of each company's stock?" (I multiplied the old price by a factor based on the percent increase or decrease in price.)
• "How did you determine the total value of the stock for each company?" (I multiplied the new price by the number of shares owned.)
• "How did you determine whether the portfolio increased or decreased in value?" (I added up the total values of the stocks for each company and compared the total using the old prices with the total using the new prices.)
• "Why did the sports clothing company lose more money than the airline company even though the airline company had a greater percentage decrease in price?" (Since the portfolio contained more shares of the sports clothing company, a smaller percent change in price resulted in a greater magnitude of change in dollars.)

In this activity, students model making an investment in the stock market when they create their own portfolio of stocks from a given list of fictional companies and a budget of $100 (MP4). Students are then told the change in each stock's price after 3 months and determine a new value of their portfolio.

The purpose of this discussion is for students to discuss the different ways to think about the change in value of their stocks. If possible, display the list of "Changes in Stock Prices after 3 Months," and discuss the following questions:

• "How can you tell if the price of a stock increased or decreased from looking at this list?" (Positive numbers represent an increase in price, while negative numbers represent a decrease in price.)
• "Which company's stock price increased or decreased the most?" (The biotechnology company's stock price increased by $37.26.)
• "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."