Illustrative Mathematics Grade 8, Unit 7, Lesson 12: Applications of Arithmetic with Powers of 10

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Illustrative Math
Grade 8

Lesson 12: Applications of Arithmetic with Powers of 10

Let’s use powers of 10 to help us make calculations with large and small numbers.

Illustrative Math Unit 8.7, Lesson 12 (printable worksheets)

Lesson 12 Summary

Powers of 10 can be helpful for making calculations with large or small numbers. For example, in 2014, the United States had 318,586,495 people who used the equivalent of 2,203,799,778,107 kilograms of oil in energy. The amount of energy per person is the total energy divided by the total number of people.

We can use powers of 10 to estimate the total energy as 2 · 10¹² and the population as 3 · 10⁸.

So the amount of energy per person in the U.S. is roughly (2 · 10¹²) ÷ (3 · 10⁸)

That is the equivalent of 2/3 · 10⁴ kilograms of oil in energy. That’s a lot of energy—the equivalent of almost 7,000 kilograms of oil per person!

In general, when we want to perform arithmetic with very large or small quantities, estimating with powers of 10 and using exponent rules can help simplify the process. If we wanted to find the exact quotient of 2,203,799,778,107 by 318,586,495, then using powers of 10 would not simplify the calculation.

Lesson 12.1 What Information Do You Need?

What information would you need to answer the following questions?

1. How many meter sticks does it take to equal the mass of the Moon?
2. If all of these meter sticks were lined up end to end, would they reach the Moon?

• See Video for Whole Lesson

Lesson 12.2 Meter Sticks to the Moon

1. How many meter sticks does it take to equal the mass of the Moon? Explain or show your reasoning.
2. Label the number line and plot your answer for the number of meter sticks.
3. If you took all the meter sticks from the last question and lined them up end to end, will they reach the Moon? Will they reach beyond the Moon? If yes, how many times farther will they reach? Explain your reasoning.
4. One light year is approximately 10¹⁶ meters. How many light years away would the meter sticks reach? Label the number line and plot your answer.

Are you ready for more?

Here is a problem that will take multiple steps to solve. You may not know all the facts you need to solve the problem. That is okay. Take a guess at reasonable answers to anything you don’t know. Your final answer will be an estimate.

If everyone alive on Earth right now stood very close together, how much area would they take up?

Lesson 12.3 That’s a Tall Stack of Cash

In 2016, the Burj Khalifa was the tallest building in the world. It was very expensive to build.
Consider the following question: Which is taller, the Burj Khalifa or a stack of the money it cost to build the Burj Khalifa?

1. What information would you need to be able to solve the problem?
2. Record the information your teacher shares with the class.
3. Answer the question “Which is taller, the Burj Khalifa or a stack of the money it cost to build the Burj Khalifa?” and explain or show your reasoning.
4. Decide what power of 10 to use to label the rightmost tick mark of the number line, and plot the height of the stack of money and the height of the Burj Khalifa.
5. Which has more mass, the Burj Khalifa or the mass of the pennies it cost to build the Burj Khalifa? What information do you need to answer this?
6. Decide what power of 10 to use to label the rightmost tick mark of the number line, and plot the mass of the Burj Khalifa and the mass of the pennies it cost to build the Burj Khalifa.

Lesson 12 Practice Problems

1. Which is larger: the number of meters across the Milky Way, or the number of cells in all humans? Explain or show your reasoning. Some useful information:

• The Milky Way is about 100,000 light years across.
• There are about 37 trillion cells in a human body.
• One light year is about meters.
• The world population is about 7 billion.

2. Ecologists measure the body length and wingspan of 127 butterfly specimens caught in a single field.
3. Diego was solving an equation, but when he checked his answer, he saw his solution was incorrect. He knows he made a mistake, but he can’t find it. Where is Diego’s mistake and what is the solution to the equation?
4. The two triangles are similar. Find x.

The Open Up Resources math curriculum is free to download from the Open Up Resources website and is also available from Illustrative Mathematics.

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