Adding and Subtracting Decimals

Add and subtract decimal numbers by lining up decimal points

The Golden Rule

Always line up the decimal points!

Example: $3.45 + 12.8$

&\phantom{0}3.45 \\ + &12.80 \\ \hline &16.25 \end{align}$$ **Tip:** Add zeros as placeholders to help line up! ## Subtracting Decimals **Example:** $15.6 - 7.38$ $$\begin{align} &15.60 \\ - &\phantom{0}7.38 \\ \hline &\phantom{0}8.22 \end{align}$$ ## Money Problems Decimals are used with money all the time! **Example:** You have $\$20.00$ and spend $\$12.75$. How much is left? $$20.00 - 12.75 = \$7.25$$ ## Word Problems 1. **Read carefully** to know if you add or subtract 2. **Line up decimal points** 3. **Check your answer** - does it make sense?

Calculate: $5.6 + 2.8$

💡 Show Solution

Solution:

Line up the decimal points:

&5.6 \\ + &2.8 \\ \hline &8.4 \end{align}$$ **Answer:** $8.4$

Sarah ran 3.75 miles on Monday and 5.4 miles on Tuesday. How many total miles did she run?

💡 Show Solution

Solution:

Add the distances:

&3.75 \\ + &5.40 \\ \hline &9.15 \end{align}$$ **Answer:** 9.15 miles

Tom had $\$ 50.00 $. He bought a book for$ $12.95 $and a toy for$ $18.50$. How much money does he have left?

💡 Show Solution

Solution:

Step 1: Find total spent

&12.95 \\ + &18.50 \\ \hline &31.45 \end{align}$$ Step 2: Subtract from original amount $$\begin{align} &50.00 \\ - &31.45 \\ \hline &18.55 \end{align}$$ **Answer:** $\$18.55$

Review key concepts with our flashcard system

Explore other calculus topics