Addition with Money

Adding with money is often students' introduction to addition with decimals.  The rule are exactly the same as adding with decimals:

• Line up the decimals before you add!
• Remember that any number without a decimal has an invisible decimal after the right-most digit (so, 72 is actually 72. or 72.00).
• If some numbers have digits behind the decimal (cents) and others don't, put in that invisible decimal and place holder zeros for the cents.
• Make sure to bring the decimal down into the answers.

Once you make sure you follow the rules above, you just add.

Example:

$3.56 + $7 = 

First, set the problem up vertically, lining up the decimal.  When there's no decimal shown, remember, it's right behind the whole number.

$$\eqalign{3&.56\\+7&\\\hline\qquad}$$

It's often easier to fill in the invisible decimal and place holder zeros before lining up.

$$\eqalign{3&.56\\+7&.00\\\hline\qquad}$$

Then, just add.

$$\eqalign{3&.56\\+7&.00\\\hline 10&.56}$$

Working with money is often a great intro to working with decimals because students often understand, conceptually, the difference between dollars and cents better than they understand the more abstract difference between whole numbers and decimal numbers. Understanding how to line up money problems can be a great, tangible intro to adding with decimals.