Illustrative Mathematics Grade 2, Unit 4: Addition and Subtraction on the Number Line
In this unit, your child uses the number line, a line with numbers equally spaced like a ruler, to add and subtract within 100. Each number is a distance from 0, and each jump shows part of a story. They solve story problems about length the same way. It connects the measuring from before to the numbers to 1,000 that come next.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 4?
- Solving story problems about lengths, such as two ribbons laid end to end, and showing them on a number line. Learn more: Story problems about length
- Placing numbers on a number line as distances from 0 and adding or subtracting with jumps of tens and ones. Learn more: Adding and subtracting on a number line
Sample questions to try together
These are real questions from our 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
A piece of yarn is 40 cm long. If you add another 30 cm piece to it, what is the total length of the yarn?
- 10 cm
- 70 cm
- 60 cm
How you can help
- Draw a number line from 0 to 100 with chalk on a sidewalk and jump forward and back by tens, then by ones.
- Tell a ribbon story: "We had 45 inches of ribbon and used 18 for a bow. How much is left?" Let your child show the jumps.
- Mark a number like 37 on a paper number line and ask how far it is from 0, from 40, and from 50.
Where kids can get stuck
- Spacing the marks unevenly, so equal jumps look like different sizes.
- Counting the mark they start on, so 52 − 5 lands on 48 instead of 47.
- Drawing a short bar for a big number and a long bar for a small one, so the picture misleads.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- number line
- A line with numbers in order at equal spaces, used to count, add, and subtract.
- distance
- How far it is from one point to another.
- jump
- A move along a number line that shows adding or subtracting.
- equally spaced
- With the same distance between every mark.
- tick mark
- A short line on a ruler or number line that marks a number.
- total length
- How long things are when they are put end to end.
- unknown
- The missing number in a problem, often shown with a box or a question mark.
Want to help your child master the number line?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
Join the club
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.
Which math standards does Illustrative Mathematics Grade 2 Unit 4 cover?
Illustrative Mathematics Grade 2 Unit 4 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.