Lesson: Meet the Megalodon

To solve the problems in this lesson, students will need to know how to convert percents to decimals. Create a matching game where students match percentages with their decimal equivalents. You can create a digital version or use sticky notes/note cards for your values. Afterward, discuss how to add, subtract, and multiply decimals. Use the decimals from the game to practice a few examples as a class.

Ask volunteers to share what they know and how they feel about sharks. Then play the video. After watching, hold a class discussion about what students learned about sharks and whether or not their perceptions of sharks have changed.

As a class, discuss the terms fact and inference. Tell students that facts are things that are definitely true while inferences are educated guesses based on facts. For example, if you know for a fact that Katya ate a turkey sandwich in the cafeteria, you might infer that Katya was hungry or that it was her lunch block. Then tell students that in the article they are about to read, scientists use facts to draw inferences. Display a T-chart with one column labeled “Fact” and the other “Inference.” Have volunteers read paragraphs of the article aloud to the class. After each paragraph, have students identify any facts that have been given as well as any corresponding inferences the scientists have made based on those facts. Record these in the chart for students to review.

Read through the introduction and the example of the “Using Percent Change” box on page 21. Discuss the following questions after each step:

• After Step 1, ask: How do you convert a percent to a decimal? (Divide 220% by 100 or move the decimal point two places to the left.)
• After Step 2, ask: What does the 1 in the equation represent? (100%) Why did you add 2.2 to 1? (Since the megalodon was 220% larger than the great white shark, you add 220% of the great white shark’s size to its original size, which is represented by 1. If the number were decreasing, you would subtract from 1. How would the expression change if the number were decreasing? (You would subtract 2.2 from 1; 1 – 2.2 = -1.2) 

Have students examine the steps in the “Using Percent Change” box on page 21. Ask them to use these steps to write out a percent change formula for finding the new amount, given an original amount. Then have students manipulate the formula so that the percent change is isolated, and then again so that the original amount is isolated. They now have three different formulas to determine different variables in a percent change problem. Then provide students with a few scenarios to practice using these formulas or distribute the “Using Percent Change” skills sheets.

Present two fictional characters to your students: Alec and Jami. In June, Alec is 62 inches tall. Each month, he gets 1.5% taller. How tall is he in July? August? September? Jami is 54 inches tall in June. She gets 2.5% shorter each month. How tall is Jami in July? August? September? Have students solve for each scenario. Then ask students to create their own fictional character and write 3 percent change questions about them and solve.