Apply Mental Strategies to Subtract within 20

Students will use mental math strategies — such as think addition, counting up, and fact families — to efficiently subtract within 20. Students connect subtraction to known addition facts to build fluency.

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Grade 2 · Addition and Subtraction Fluency within 20 · question 1 of 3

0 of 12

12 rungs. A star at the top.

12 − 4 =

How it is taught

0:00 of 3:13

Subtraction undoes addition.

Think the missing addend.

Read it: Back through 10

14 − 6. 14 is 10 and 4. Take the 4 first to get to 10, then 2 more: 8. So 14 − 6 = 8.

Split the 6 into 4 and 2.
Take 4: back to 10.
Take 2 more from the 10: 8.

The 4 ones are not enough to take 6, so go back to 10 first.

10 is easy to take from: 10 − 2 = 8.

It is make 10, backwards: 14, then 10, then 8.

Take the ones to get back to 10. Then take the rest from the 10.

Taking 4 from 6 instead, because 6 − 4 is easy, and writing 12.

There are only 4 ones. Take them, then 2 more from the 10: 8.

13 − 7 = ___ — 6. Take 3 to get to 10, then 4 more: 6.

14 − 8

You have fourteen stickers and you give eight to a friend. How many are left?

We need to find fourteen minus eight.

Here's a clever trick — instead of subtracting, think addition. Eight plus what equals fourteen?

Let's count up from eight to fourteen on a number line.

First, jump from eight up to ten. That's a jump of two.

Then jump from ten up to fourteen. That's a jump of four more.

Two plus four equals six. So eight plus six equals fourteen.

Grade 2 · Think addition to subtract

That means fourteen minus eight is six. You have six stickers left!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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