Adding and subtracting on a number line
In 2nd grade, children learn to show whole numbers as distances from 0 on a number line and to use number lines to add and subtract within 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 2nd 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
On a number line from 0 to 10, which number is closest to 0?
- 5
- 1
- 10
Why this matters
The number line is a picture your child will lean on for years. It makes mental strategies visible, such as jumping from 38 to 40 and then on to 65, and in 3rd grade it is where they learn that fractions like 1/2 and 3/4 are numbers that sit between whole numbers. Later still, it helps with rounding, negative numbers, and graphs.
Where kids can get stuck
- Counting marks instead of jumps, including the starting number, so 35 + 6 lands on 40 instead of 41.
- Spacing the marks unevenly, so distances look wrong and equal jumps appear different sizes.
- Moving the wrong way, jumping right to subtract or left to add, especially on unlabeled lines.
How you can help
- Draw a number line with chalk on the sidewalk from 0 to 20, and have your child hop along it to act out problems like 8 + 5 or 17 - 9.
- Use a measuring tape as a number line. Ask your child to find 30 inches, then add 15 more inches and say where they land.
- Sketch a quick number line on paper when adding, such as 46 + 30, and let your child show the jumps of 10 as arcs above the line.
The kid-friendly video below explains it in a few minutes, and Bobby's Math Club offers free practice that grows with your child.
Kid-friendly explanation
Questions parents ask
Why is my child using number lines to add and subtract?
Number lines show numbers as lengths from zero, which helps your child see what adding and subtracting mean: moving forward or back. They make mental strategies visible, like jumping to the nearest ten. Number lines are also important later for fractions, decimals, and negative numbers.
Why do the spaces on a number line have to be equal?
Each space stands for the same amount, like the inches on a ruler. If the spaces are uneven, the distances do not match the numbers, and the number line gives misleading answers. Learning to space marks evenly helps your child understand that the number line is a kind of measuring tool.
Does my child have to draw every number on the number line?
No. For larger numbers, children often draw an open number line, a line with only the numbers they need marked. To add 47 + 25, they might mark 47, jump 20 to 67, then jump 5 to 72. This shows their thinking without needing every mark.
Make learning math fun
Bobby's Math Club turns 2nd grade math practice into something fun to do together.
- Unlimited practice, completely free
- Practice that starts where your child is and grows with them
- 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 2.MD.B.6: “Represent whole numbers as lengths from 0 on a number line diagram with equally spaced points corresponding to the numbers 0, 1, 2, ..., and represent whole-number sums and differences within 100 on a number line diagram.” Learn how Bobby's Math Club can help your students grow. (Common Core 2.MD.6)