# 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.

## 12.1: What Information Do You Need?

What information would you need to answer these 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?

## 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 $10^{16}$ meters. How many light years away would the meter sticks reach? Label the number line and plot your answer.

## 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 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.

## 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 $$2 \boldcdot 10^{12}$$ and the population as $$3 \boldcdot 10^8$$ So the amount of energy per person in the U.S. is roughly $$2 \boldcdot 10^{12} \div 3 \boldcdot 10^8$$ That is the equivalent of $$\frac{2}{3} \boldcdot 10^4$$ 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.