Decimals are numbers that include a decimal point to show parts of a whole. When you add or subtract decimals, you are combining or comparing parts of numbers, just like with whole numbers—but you must keep the decimal points lined up.
Always line up the decimal points before adding or subtracting. You can add zeros so the numbers have the same number of decimal places.
Word problems show how decimals are used in real-life situations. Read carefully to decide what the problem is asking and whether you need to add or subtract to find the answer.
Think about what’s happening in the story. If you’re putting things together, add. If you’re finding the difference, subtract.
You add decimals when combining measurements, money amounts, or totals. Adding decimals helps you find the whole amount when parts are joined together.
Sara bought a notebook for $3.25 and a pen for $1.75. How much did she spend in all?
She spent $5.00 in total.
When adding money or measurements, make sure all values are written with the same number of decimal places before you solve.
You subtract decimals to find how much is left, how much more is needed, or the difference between two measurements or amounts.
Alex had $20.00. He spent $12.45 on lunch. How much money does he have left?
Alex has $7.55 left.
Make sure each digit is in the correct place value column (ones, tenths, hundredths). Add zeros if needed before subtracting.
Decimals appear in many real-life situations such as money, distance, weight, and time. Practicing these helps you understand how decimals are used every day.
Check your answers by estimating first. If your final answer is close to your estimate, it is likely correct.