i-Ready Classroom Mathematics Grade 1, Unit 2: Addition and Subtraction Within 20
In this unit, first graders add and subtract within 20 using making ten, doubles, and thinking of subtraction as a missing addend, the part you add to reach the total. They solve story problems, some with three numbers, check whether equations are true, and find unknown numbers. It builds on the work within 10 from the last unit and prepares them for place value and comparing numbers next.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 2?
- Solving story problems within 20 with the unknown in any position, using drawings and equations. Learn more: Adding and subtracting story problems within 20
- Adding three numbers in a story to 20, such as 5 + 8 + 2, by finding a helpful pair first. Learn more: Story problems that add three numbers
- Grouping addends in a helpful way, like adding 6 + 4 first in 6 + 9 + 4. Learn more: Adding in any order to make it easier
- Solving 16 - 9 by thinking 9 + ? = 16. Learn more: Subtracting by finding the missing part
- Adding and subtracting within 20 with make a ten and doubles, getting quicker with each fact. Learn more about adding within 20: Adding within 20 · Learn more about subtracting within 20
- Deciding whether equations like 14 = 7 + 7 and 9 + 3 = 10 + 1 are true or false. Learn more: What the equal sign really means
- Finding unknown numbers in equations like ? + 6 = 15 or 13 = 18 - ?. Learn more: Missing numbers, like 8 + ? = 11
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
I had some toy cars. My friend gave me 3 more cars. Now I have 8 cars in total. How many toy cars did I have at first?
- 3
- 5
- 8
How you can help
- Tell a three-part story at the table: "5 crackers, 8 pretzels, and 2 apple slices. How many snacks?" Ask which two numbers your child added first.
- Practice making ten with 9 spoons and 6 forks: move one fork to join the spoons and make 10, then count what's left to find 9 + 6.
- Write a puzzle on a sticky note, like ? + 6 = 15, and ask your child to explain how they found the missing number.
Where kids can get stuck
- Writing 21 for ? + 6 = 15, adding the two numbers they can see.
- Calling 9 + 3 = 12 + 1 true because 9 + 3 does make 12.
- Adding the first two numbers in a three-part story and stopping too soon.
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
- addend
- A number being added, like 3 and 4 in 3 + 4.
- make a ten
- Split a number to fill a ten first, like 8 + 5 = 8 + 2 + 3.
- doubles
- A number added to itself, like 6 + 6.
- missing addend
- The part you need to add to reach a total, like 2 in 8 + ? = 10.
- equation
- A number sentence with an equal sign, like 5 + 3 = 8.
- equal sign
- The symbol = that means "the same amount as."
- true
- An equation is true when both sides are the same amount.
- false
- An equation is false when the two sides are different amounts.
- unknown
- The number we don't know yet, shown with a box or question mark.
Want to help your child master facts to 20?
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.
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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.
Which math standards does i-Ready Classroom Mathematics Grade 1 Unit 2 cover?
i-Ready Classroom Mathematics Grade 1 Unit 2 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
- 1.OA.A.1: Use addition and subtraction within 20 to solve word problems.
- 1.OA.A.2: Solve word problems that call for addition of three whole numbers.
- 1.OA.B.3: Apply properties of operations as strategies.
- 1.OA.B.4: Understand subtraction as an unknown-addend problem.
- 1.OA.C.6: Add and subtract within 20.
- 1.OA.D.7: Understand the meaning of the equal sign.
- 1.OA.D.8: Determine the unknown whole number in an addition or subtraction equation.
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.