Adding and subtracting decimals to hundredths
In 5th grade, children learn to add and subtract decimals to hundredths, like 3.4 + 1.25 and 6 - 2.75, using drawings and place value, and to explain how a drawing matches the written steps.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 5th grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
Amara bikes 4.6 kilometers to the library and then 3.85 kilometers to the park. How far does she bike in all?
- 4.31 kilometers
- 7.45 kilometers
- 8.45 kilometers
Why this matters
Adding and subtracting decimals is the math of everyday money, so your child will use it well beyond math class. Totaling a receipt, working out change, and finding how much farther one throw went than another all depend on it. It leads into multiplying and dividing decimals later this year. And knowing that 3.4 means 3 and 4 tenths helps your child notice if a total is too small to be right.
After this comes multiplying decimals to hundredths, where your child puts the same tenths and hundredths to work in a new way.
Where kids can get stuck
- Lining up the last digits instead of the decimal points, so 3.4 + 1.25 becomes 1.59 instead of 4.65.
- Forgetting that ten tenths make a whole, so 2.6 + 1.7 comes out as 3.13 instead of 4.3.
- Subtracting the smaller digit from the larger in each place, so 5.2 - 1.75 comes out as 4.55 instead of 3.45.
How you can help
- Hand your child a receipt with three or four items and ask them to add the prices to check the total. Ask them to estimate first, so they know roughly what answer to expect.
- Work out the change before you pay. If lunch costs $7.35 and you hand over $10, ask your child how much should come back, then count up from $7.35 together to check.
- Ask your child to show 2.6 + 1.7 two ways at the table: with play money, as dollars and dimes, then written in a column. Have them point to where 10 dimes became a dollar, in the money and in the written steps.
If it’s helpful, you can sign up for free, adaptive practice in Bobby's Math Club.
Questions parents ask
Why is my child learning to add decimals by lining up place values?
Lining up the decimal points lines up the places, so tenths join tenths and hundredths join hundredths. It is the same idea your child used for ones and tens with whole numbers, carried past the decimal point. Writing 3.4 as 3.40 above 1.25 can make it clearer: 3 + 1 ones, 4 + 2 tenths, and 0 + 5 hundredths give 4.65. And if the tenths pass 9, ten of them trade for one whole.
Should my child add zeros when subtracting decimals?
It often helps. Writing 6 as 6.00 in 6 - 2.75 gives every place a digit, so your child can see the trade: 6 ones become 5 ones, 9 tenths, and 10 hundredths. The answer is 3.25. A zero at the end of a decimal doesn't change its value, so 6, 6.0, and 6.00 are the same number.
How can my child check a decimal answer?
Rounding first is a quick check. For 4.85 + 3.2, your child can think 5 + 3 = 8, so an answer near 8 makes sense, and the exact answer is 8.05. If they get 5.17, the estimate shows something went wrong, often decimal points that weren't lined up. For subtraction, adding back works too: 3.25 + 2.75 should come back to 6.
Make learning math fun
Bobby's Math Club turns 5th grade math practice into something fun to do together.
- Unlimited free practice
- A few minutes a day, at just the right level
- Hints when they are stuck, and a celebration when it clicks
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 5.NBT.B.7: “Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.” Learn how Bobby's Math Club can help your students grow. (Common Core 5.NBT.7)