While working at the zoo one day, Joshua saw a customer drop her purse and a whole pile of change came flooding out of it. Joshua ran over to help and immediately began picking up all kinds of coins. It seems that the clasp of the woman's change purse had snapped and sent money rolling over the ground.

Joshua picked up 30 pennies, 15 nickels, 10 dimes and 13 quarters. The woman was very grateful, and Joshua was glad that he had been there to help out.

When he was walking away, Joshua wondered how much money the woman had dropped. This is a perfect example of where a real - world problem and expressions can come in handy.

**Pay close attention to this Concept and you will learn how to write an expression and solve for the sum of the money.**

### Guidance

Money is a common source of dilemmas in real - life. Let's combine money and variable expressions to solve a real - world problem.

Joanne has a pile of nickels and a pile of dimes. She counts her money and figures out that she has 25 nickels and 36 dimes. Given these counts, how much money does Joanne have in all?

**The first thing that we need to do is to underline all of the important information in the problem.**

Joanne has a pile of nickels and a pile of dimes. She counts her money and figures out that she has 25 nickels and 36 dimes. Given these counts, how much money does Joanne have in all?

**Next, we need to write an expression with a variable.**

\begin{align*} .05x +.10y \end{align*}

A nickel is 5 cents. We can use decimal .05 to show that amount in dollars.

A dime is 10 cents. We can use decimal .10 to show that amount in dollars.

The \begin{align*}x\end{align*} represents the number of nickels.

The \begin{align*}y\end{align*} represents the number of dimes.

We have been given the number of dimes and nickels that Joanne has. We can substitute those values into our expression for \begin{align*}x\end{align*} and \begin{align*}y\end{align*}.

\begin{align*}.05(25) + .10(36)\end{align*}

**Next, we evaluate the expression.**

\begin{align*}1.25 + 3.60 = \$4.50\end{align*}

**Joanne has** \begin{align*}\$4.50\end{align*} **total. You can see why we changed the way we wrote the value of coins from cents to dollars now, because our answer is in dollars.**

**Use the expression that Joanne used to figure out the following totals.**

#### Example A

If you have 6 nickels and five dimes, what is the sum?

\begin{align*} .05x +.10y \end{align*}

**Solution: .80**

#### Example B

If you have 15 nickels and 20 dimes, what is the sum?

\begin{align*} .05x +.10y \end{align*}

**Solution: $2.75**

#### Example C

If you have 35 nickels and 40 dimes, what is the sum?

\begin{align*} .05x +.10y \end{align*}

**Solution: $5.75**

These examples are the perfect practice for helping Joshua with his dilemma. Let's look at the original problem once again.

While working at the zoo one day, Joshua saw a customer drop her purse and a whole pile of change came flooding out of it. Joshua ran over to help and immediately began picking up all kinds of coins. It seems that the clasp of the woman's change purse had snapped and sent money rolling over the ground.

Joshua picked up 30 pennies, 15 nickels, 10 dimes and 13 quarters. The woman was very grateful, and Joshua was glad that he had been there to help out.

When he was walking away, Joshua wondered how much money the woman had dropped.

First, Joshua will need to write an expression to explain the money that was found. Joshua picked up pennies, nickels, dimes and quarters. Begin by writing the worth of each coin in the expression.

\begin{align*} .01x +.05y + .10z + .25q \end{align*}

Next, substitute the number of each coin found.

\begin{align*} .01(30) +.05(15) + .10(10) + .25(13) \end{align*}

Finally, evaluate the expression for the sum of the dropped money.

**The answer is \begin{align*}\$5.30\end{align*}.**

### Vocabulary

- Evaluate
- to simplify an expression that does not have an equals sign.

- Variable
- a letter, usually lowercase, that is used to represent an unknown quantity.

- Expression
- a number sentence that uses operations but does not have an equals sign

- Variable Expression
- a number sentence that has variables or unknown quantities in it with one or more operations and no equals sign.

### Guided Practice

Here is a problem for you to try on your own. Use the given information to write an expression and solve for the sum.

Imagine that you have found a pile of money in a drawer. In it, you have 10 nickels, 5 dimes and 15 quarters. How much is the sum of the money that you have found?

**Answer**

First, you have to write an expression. Nickels are worth .05, dimes are worth .10 and quarters are worth .25. Now you can write an expression.

\begin{align*} .05x +.10y + .25z \end{align*}

Next, you can substitute in the numbers of each coin that we found. You found 10 nickels, 5 dimes and 15 quarters.

\begin{align*} .05(10) +.10(5) + .25(15) \end{align*}

\begin{align*} .50 + .50 + 3.75 \end{align*}

**Our total is \begin{align*}\$4.75\end{align*} .**

### Video Review

Khan Academy Evaluating an Expression

James Sousa Example of Evaluating an Expression

James Sousa Example of Evaluating an Expression

### Practice

Directions: Write an expression for each money amount and evaluate it by using the given information.

1. 15 quarters

2. 10 dimes and 3 quarters

3. 30 nickels and 15 dimes

4. 6 quarters and 60 nickels

5. 21 quarters and 14 dimes

6. 6 dimes, 10 nickels and 120 pennies

7. 18 quarters and 12 half - dollars.

8. 32 dimes, 16 nickels and 11 quarters

9. 18 nickels, 33 dimes and 39 quarters

10. 27 dimes, 87 pennies, 12 quarters

11. 10 pennies, 15 nickels, 9 dimes and 27 quarters

12. 35 quarters and 98 nickels

13. 95 dimes, 27 nickels and 82 quarters

14. 77 dimes, 15 nickels and 81 quarters

15. 70 nickels, 63 dimes, 82 pennies and 55 quarters

16. 12 nickels, 33 dimes, 17 pennies and 80 quarters