1st Grade Subtraction Within 20 Lesson (Free PDF)
This subtraction within 20 lesson for 1st Grade covers subtraction within 20 (Common Core 1.OA.A.1, 1.OA.B.4, 1.OA.C.6), with a free PDF to print.
Subtraction takes a part away from a whole, or finds how many more one group has than another. The answer is the difference. In first grade you subtract within 20 by counting back, by thinking of the missing addend, and by using fact families, so 13 – 5 = 8 because 5 + 8 = 13.
Grade 1 · Common Core State Standards: 1.OA.A.1, 1.OA.B.4, 1.OA.C.6
Key facts in this subtraction within 20 lesson
- The difference is the answer to a subtraction problem.
- Counting back: hop back from the whole, one number at a time.
- Think addition: 13 – 5 asks what to add to 5 to get 13.
- A fact family uses three numbers, like 8, 7 and 15.
- Subtracting 0 or the whole number gives easy answers: 6 – 0 = 6 and 6 – 6 = 0.
What is subtraction?
Subtraction means taking some away, taking a group apart, or finding how many more or fewer. The answer is called the difference. We use a minus sign: \(9 – 4 = 5\).
How do you count back?
Start at the whole number. Hop back one at a time. Stop after you have hopped the number you subtract.
How can addition help you subtract?
Think of a missing part. To find \(13 – 5\), ask: what do I add to 5 to get 13? The missing part is 8, because \(5 + 8 = 13\). So \(13 – 5 = 8\).
How do you subtract through ten?
When the numbers are big, use ten as a stepping stone. Break the small number into two parts.
- Subtract the ones to reach 10.
- Subtract what is left of the small number from 10.
Example: \(14 – 6\). First \(14 – 4 = 10\). Then take 2 more: \(10 – 2 = 8\). So \(14 – 6 = 8\). You can check the answer by adding: \(8 + 6 = 14\). If the check works, the answer is right.
What is a fact family?
A fact family uses the same three numbers. Two addition facts and two subtraction facts tell the same story.
How do you compare two groups?
Line the groups up. The extra counters show how many more one group has. Subtract to find the difference.
Here \(11 – 6 = 5\), so the blue row has 5 more.
Subtraction within 20 lesson: questions and answers
What is the difference in subtraction?
The difference is the answer to a subtraction problem. In 12 – 5 = 7, the difference is 7. It tells how many are left or how many more.
How can I use addition to subtract?
Turn the problem into a missing addend. For 14 – 6, ask 6 + ? = 14. The missing number is 8, so 14 – 6 = 8.
What is a fact family?
A fact family is a set of addition and subtraction facts that use the same three numbers. For 4, 9 and 13: 4 + 9 = 13, 9 + 4 = 13, 13 – 4 = 9, 13 – 9 = 4.
How do I compare two groups?
Match the items one to one. Count the extras, or subtract the smaller number from the larger. If one team has 12 and another has 9, then 12 – 9 = 3 more.
What happens when I subtract zero?
Nothing changes. 8 – 0 = 8. If you subtract the whole number, you get zero, like 8 – 8 = 0.
How to use this subtraction within 20 lesson
Read the definitions first, then follow the worked method line by line and redo the example on paper without looking. When every step makes sense, move on to the worksheet, then check yourself with the quiz.
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All Grade 1 chapters: Grade 1 math.
