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## 2nd grade

### Course: 2nd grade > Unit 1

Lesson 4: Add and subtract within 20- Adding within 20 using place value blocks
- Adding within 20 using ten frames
- Subtract within 20 using place value blocks
- Subtract within 20 using a number line
- Add & subtract within 20
- Addition and subtraction word problems: gorillas
- Addition and subtraction word problems: superheroes
- Add and subtract within 20 word problems

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# Subtract within 20 using place value blocks

Sal subtracts 13-4 using place value blocks. Created by Sal Khan.

## Want to join the conversation?

- Think of 13-3, then subtract one more.

13-4=9.(1 vote)

- How do you do 40 -10 in 10's frame(0 votes)
- 40 − 10 = 4 tens − 1 ten = 3 tens = 30(2 votes)

- How will you subtract 10−7(0 votes)
- you count on your fingers or look at this.

10-7=3(0 votes)

## Video transcript

- [Instructor] Let's see
if we can think about what number is equal to 13 minus four, and to help us think about that, let's look at 13 blocks here. And the way that it's been set up, you can see that 10 have been arranged in this bar over here. One, two, three, four, five,
six, seven, eight, nine, 10 and that makes sense because 13 is one 10 and three ones. One 10 and one, two, three ones. So this right over here
is a total of 13 blocks. Now, if we're subtracting four, we're gonna take four
of those blocks away. So let's do that. We'll take away this one, that's one, two, three, and then we'd
have to take one away and break this group of 10. And so, how many do we have left? Well, we can see very clearly we have one, two, three, four, five,
six, seven, eight, nine left and so we could write a
nine right over there. Another way to think about it is if you take away three, you're
just left with this bar of 10 and then you have take away one more and then you are left with nine.