In this lesson, students see how signed numbers can be applied to representing changes in the stock market (MP4). This includes representing a decrease (in the price of an individual stock or the value of a stock portfolio) as a negative percentage of the original value.

First, students calculate the original price, new price, change, or percent change for several individual stocks. Then, they calculate how much the value changed for a portfolio of multiple stocks. The company names given in this lesson are generic. The data is based on real stock market data from 2016. The teacher may wish to replace them with up-to-date data from real companies.

The last activity is optional because it provides an opportunity for additional practice applying operations with rational numbers. Students select stocks to create their own portfolio and then calculate whether the value of their portfolio increases or decreases. This activity could be extended to last across multiple weeks if using real data.