This grade 1 subtraction within 20 lesson explains subtraction within 20 in one printable page, with definitions, a method and a worked example.
Subtraction takes a part away from a group to find how many are left. The answer is called the difference. In Grade 1, children subtract within 20 by counting back, thinking of a missing addend, and using fact families. For example, \(13-8\) is the same as asking \(8+\text{ ? }=13\), and the answer is 5.
Grade 1 Subtraction Within 20 Lesson: key facts
- Subtraction means taking away, like \(8-3=5\). The answer is the difference.
- Counting back: start at the first number and count down the second number.
- Think addition: \(13-8\) asks \(8+\text{ ? }=13\). The missing part is 5.
- To compare, match the groups. The extra objects show how many more or fewer.
- A fact family uses three numbers in four sentences, like 6, 9, and 15.
What does it mean to subtract?
To subtract means to take away, or to find how many are left. The minus sign – means "take away." Liam has 8 grapes. He eats 3 grapes. Cross out 3 of the 8. Five are left, so \(8-3=5\). The answer to a subtraction problem is called the difference.
A subtraction sentence uses – and =, like \(9-4=5\). The first number is the whole. The second number is the part taken away.
How does counting back work?
Counting back is a quick way to take away a small number. Start at the first number. Then count down. To find \(10-3\), say 10, then count back 9, 8, 7. Hop back on a number line one step for each count. You land on 7.
How can addition help you subtract?
Subtraction can be a missing-part problem. To find \(10-7\), ask: 7 plus what number makes 10? The missing part is 3, so \(10-7=3\).
- Look at \(13-8\). Ask: 8 plus what makes 13?
- From 8, count up to the next ten: \(8+2=10\).
- From 10, count up to 13: \(10+3=13\).
- Add the jumps: \(2+3=5\).
- Check: \(8+5=13\). So \(13-8=5\).
How do you compare two groups?
Sometimes a problem asks how many more or how many fewer. Line up the two groups. Match one to one. The cubes with no match are the difference. Mei has 9 blue cubes and Jamal has 5 green cubes. Four blue cubes have no match, so Mei has 4 more. Jamal has 4 fewer. We write \(9-5=4\).
What is a fact family?
A fact family uses the same three numbers in addition and subtraction. The numbers 6, 9, and 15 make four sentences: \(6+9=15\), \(9+6=15\), \(15-9=6\), and \(15-6=9\). If you know one fact, you know all four.
Subtraction Within 20: frequently asked questions
What is the difference in a subtraction problem?
The difference is the answer when you subtract. In \(12-5=7\), the difference is 7. It tells how many are left or how many more.
How can addition help with subtraction?
Subtraction is a missing-part problem. To find \(14-6\), ask what number added to 6 makes 14. Since \(6+8=14\), the answer is 8.
How do you find how many more?
Line up the two groups and match them. The objects with no match are the difference. If one group has 11 and the other has 6, then \(11-6=5\), so one group has 5 more.
What is a fact family?
A fact family is a set of addition and subtraction sentences with the same three numbers. For 7, 8, and 15, the sentences are \(7+8=15\), \(8+7=15\), \(15-8=7\), and \(15-7=8\).
What is 0 taken away from a number?
Nothing changes. Taking away 0 leaves the same number, so \(9-0=9\). Taking away the whole number leaves 0, so \(9-9=0\).
How to use this grade 1 subtraction within 20 lesson
Use this grade 1 subtraction within 20 lesson before the worksheet, then check what you learned with the quiz.
See every chapter on the Grade 1 math page.