Adding tenths and hundredths together
In 4th grade, children learn to rename tenths as hundredths, like 3/10 = 30/100, and to add a tenths fraction and a hundredths fraction together, such as 3/10 + 4/100.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 4th 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
How many hundredths make the same amount as 1/10?
- 1
- 10
- 100
Why this matters
Tenths and hundredths are your child's bridge from fractions to decimals, and money makes the link plain: a dime is a tenth of a dollar and a penny is a hundredth. Renaming 3/10 as 30/100 is what makes 0.3 and 0.30 the same amount, which they need when writing and comparing decimals this year. In 5th grade it grows into adding any fractions with different denominators.
Where kids can get stuck
- Adding tops and bottoms straight across, writing 3/10 + 4/100 = 7/110, without first renaming the tenths as hundredths.
- Renaming 3/10 as 3/100, changing the bottom to 100 but not multiplying the top by 10.
- Thinking 4/100 is larger than 3/10 because both of its numbers are bigger, not seeing that hundredths are tiny pieces.
How you can help
- Count coins at home with dimes and pennies. Ask your child to show 2 dimes and 7 pennies, write the amount as 20/100 + 7/100, and find the total of 27/100 of a dollar.
- Draw a 10 by 10 grid on paper and shade 4 full columns. Ask your child to name the shaded part as tenths and as hundredths, explaining why both names fit.
- At a store, look at a price like $0.65 together. Ask how many dimes and pennies make it, then say it as 6 tenths and 5 hundredths of a dollar.
For more, Bobby's Math Club has free practice at your child’s level.
Questions parents ask
Why is my child learning tenths and hundredths this way?
Tenths and hundredths connect neatly, since every tenth is exactly 10 hundredths. Teachers use grids of 100 squares and coins to show this, so your child can see that 3/10 and 30/100 cover the same amount. Once that makes sense, adding 3/10 and 4/100 is a matter of renaming and counting. It also prepares your child to understand decimals, which use the same places.
Why can my child add tenths and hundredths but not other fractions with different denominators?
Tenths and hundredths are a special case because they line up with place value, the same base-ten system your child uses for whole numbers. That makes renaming 3/10 as 30/100 easy to picture with money or grids. Adding fractions like 1/3 + 1/4 needs a more general method for finding common denominators, which your child learns in 5th grade.
How does this connect to money?
A dime is one tenth of a dollar, and a penny is one hundredth. So 3/10 of a dollar is 3 dimes, which is also 30 pennies, or 30/100. Adding 3/10 + 4/100 is like counting 3 dimes and 4 pennies, which makes 34 cents. Many children find fractions easier to picture when they can think of coins.
Make learning math fun
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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 4.NF.C.5: “Express a fraction with denominator 10 as an equivalent fraction with denominator 100, and use this technique to add two fractions with respective denominators 10 and 100. For example, express 3/10 as 30/100, and add 3/10 + 4/100 = 34/100.” Learn how Bobby's Math Club can help your students grow. (Common Core 4.NF.5)