9.2 Solve money applications

Solution

Step 1. Read the problem. Make sure you understand all the words and ideas.

• Determine the types of coins involved.

Think about the strategy we used to find the value of the handful of coins. The first thing you need is to notice what types of coins are involved. Adalberto has dimes and nickels.

• Create a table to organize the information.
  • Label the columns ‘type’, ‘number’, ‘value’, ‘total value’.
  • List the types of coins.
  • Write in the value of each type of coin.
  • Write in the total value of all the coins.

We can work this problem all in cents or in dollars. Here we will do it in dollars and put in the dollar sign ($) in the table as a reminder.

The value of a dime is $\text{\$0.10}$ and the value of a nickel is $\text{\$0.05}.$ The total value of all the coins is $\text{\$2.25}.$

Step 2. Identify what you are looking for.

• We are asked to find the number of dimes and nickels Adalberto has.

Step 3. Name what you are looking for.

• Use variable expressions to represent the number of each type of coin.
• Multiply the number times the value to get the total value of each type of coin.
  In this problem you cannot count each type of coin—that is what you are looking for—but you have a clue. There are nine more nickels than dimes. The number of nickels is nine more than the number of dimes.
  $\text{Let}d=\text{number of dimes.}$
  $d+9=\text{number of nickels}$
  Fill in the “number” column to help get everything organized.

Now we have all the information we need from the problem!

You multiply the number times the value to get the total value of each type of coin. While you do not know the actual number, you do have an expression to represent it.

And so now multiply ${\text{number}}·{\text{value}}$ and write the results in the Total Value column.

Step 4. Translate into an equation    . Restate the problem in one sentence. Then translate into an equation.

Step 5. Solve the equation using good algebra techniques.

Write the equation.
Distribute.
Combine like terms.
Subtract 0.45 from each side.
Divide to find the number of dimes.
The number of nickels is d + 9

Step 6. Check.

$\begin{array}{ccc}12\text{dimes:}12\left(0.10\right)\hfill & =\hfill & 1.20\hfill \\ 21\text{nickels:}21\left(0.05\right)\hfill & =\hfill & \underset{\text{\_\_\_\_\_}}{1.05}\hfill \\ & & \text{\$2.25}✓\hfill \end{array}$

Step 7. Answer the question.

$\mathit{\text{Adalberto has twelve dimes and twenty-one nickels.}}$

If this were a homework exercise, our work might look like this:

Check:

$\begin{array}{cccccc}\text{12 dimes}\hfill & & & \hfill 12\left(0.10\right)& =\hfill & 1.20\hfill \\ \text{21 nickels}\hfill & & & \hfill 21\left(0.05\right)& =\hfill & \underset{\text{\_\_\_\_\_}}{1.05}\hfill \\ & & & & & \text{\$2.25}\hfill \end{array}$