Video: Subtraction within 20 by Counting Backward

In this video, we will learn how to count back to find the difference between two numbers within 20.

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Video Transcript

Subtraction within 20 by Counting Back.

In this video, we will learn how to count back to find the difference between two numbers within 20. We can count back on a number line to help us take away. To take away on a number line, we start with the first number. If we’re doing 15 take away five, we start at number 15. And we have to take away five. So we need to count back five places on the number line: one, two, three, four, five. 15 take away five is 10. We started at number 15. We counted back or took away five. We finished on number 10. So if we want to subtract, we can count back.

Subtracting or taking away is the same as counting back in our heads or on a number line. To subtract, we count back. Let’s practice with an example.

Isabella put her counter on 12 then moved it back two spaces. 10 is two less than 12. Help her find the missing number. What is three less than 16?

We’re looking for the number that is three less than 16. So Isabella needs to put her counter on number 16. We need to find the number which is three less than 16. So we need to count back three places: one, two, three. The counter landed on number 13. 16 take away three is 13. Or we could say that 13 is three less than 16. We started at number 16 on the number line and counted back three spaces, because counting back is the same as subtracting.

In this video, we’ve learned how to count back to find the difference between two numbers within 20.

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