Main content

## Class 1

### Course: Class 1 > Unit 1

Lesson 5: Making 10# Getting to 10 by filling boxes

Sal shows how to add two numbers to make 10. He uses 3 + ___ = 10 and 6 + ___ = 10 as examples.

## Want to join the conversation?

- How can we subtract larger numbers off our fingers?(0 votes)
- Once you advance into higher levels, you will not need to utilize your fingers anymore, but a great strategy for now is to benchmark to 10.

If you don't know what I mean, here's an example:

I want to subtract 26-19 with my fingers.

So, first, you have to find the closest high multiple of 10 (from the number that you are going to subtract, in this case 19), which is 20. If you don't get this, it's just like 13 and 20 too, and 46 and 50. So always a multiple 10 above the number. And now you have to use that multiple of 10 (in this case 20) and subtract it by the original number (in this case 19). Well that's easy: we all know that 20-19= 1. And then, go higher and higher to reach the first number (this one's 26) and from 20-26, it's 6. So 6+1 (from 19) = 7.

And there you have it! 26-19=7!

Hope this helps!(9 votes)

- Using boxes is a great way of being more accurate when solving problems like these. However, to graph a box and then plug in the data will take time. Is there a way how we can mentally create a graph in our minds and then solve it or an easier method or formula to solve harder, more advanced problems like this to save time?(0 votes)
- Yes there is. 6 + ? = 10. You can just subtract 6 from ten to find out what the ? is. 10 - 6 = 4. The ? is 4. 6 + 4 = 10. Next cool thing to try: instead of having a question mark, you can have a letter. So I could have written 6 + x = 10. And then x = 10 - 6. And then x = 4. There you go, you just did algebra!(2 votes)

## Video transcript

- [Voiceover] We have three
plus blank is equal to 10. So pause the video and try to figure out what the blank is. What do I have to add
to three to get to 10? So you've had a go at it. Now let's see if we can do this together. So over here, I have three of these, I guess you could say purple,
these purple pinkish circles and I have 10 boxes. One, two, three, four, five, six, seven, eight, nine, ten. So one way to think about it is, how many more circles do
I need to add to fill up all of the boxes? Well, let's just count that together. I need to add one, two, three, four, five, six, seven to fill up all 10 boxes. So three plus what is equal 10? Well, three plus one, two,
three, four, five, six, seven. is equal to 10. Let's do one more of these. So now I have six plus
blank is equal to 10. So again, try to pause the video and see if you can figure
out what the blank is. What do I need to add to six to get to 10? Let's do it together. So we now have one, two,
three, four, five, six circles. We have 10 boxes here. One, two, three, four, five,
six, seven, eight, nine, ten. So we just have to think
about how many more circles do we need to fill up all
the boxes to get to 10 because we already have six filled in. Well, we need one, two,
three, four to get to 10. So let's just fill that in. Six plus four is equal to 10, or we could say even that four plus six is equal to 10, either way.