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### Course: Arithmetic (all content)>Unit 2

Lesson 2: 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?
• 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!
• 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?