Skill: Solve money problems with decimals

Money amounts use decimals: the digits to the left of the decimal are dollars, and the two digits to the right are cents. Always line up decimal points when adding or subtracting.

Example: A student buys 3 notebooks at 2.45$each and a pen for$$1.79$. If the student pays with$$10.00$, how much change will they receive?

First, find the cost of the notebooks:

$$\begin{aligned} 2.45\\ \times 3\\ \hline 7.35 \end{aligned}$$

So, 3 notebooks cost 7.35$.

Now add the cost of the pen. Line up the decimal points:

$$\begin{aligned} 7.35\\ + 1.79\\ \hline 9.14 \end{aligned}$$

The total cost is 9.14$.

Finally, subtract the total from the amount paid:

$$\begin{aligned} 10.00\\ - 9.14\\ \hline 0.86 \end{aligned}$$

The student receives 0.86$ in change.

Check the answer by estimating: 2.50 \approx $7.50)$, and$$7.50+$1.80\approx $9.30$. Since$$10.00-$9.30\approx $0.70$, an answer of$$0.86$ is reasonable.