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Using Mental Math to Add

Using Mental Math to Add

Author: Drew Watson

I can add two-digit numbers by using mental math.

Students will learn how to add two-digit numbers by using only mental math. One such strategy they will learn in this lesson is splitting or decomposing "unfriendly" numbers into smaller parts, and then adding those parts to the other number that hasn't been split.

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Let's take the original problem: 25 +14 = ?

In order to use mental math and do this in our head, we'll need to first decompose the "unfriendly" number. 

14 is the same thing as 10  + 4, but now it's a friendly number because the tens are much easier to count by on a number line.

So what would 25 + 10 be? 35...but we still have that pesky 4 left over? So go ahead and add that to 35. 35 + 4 = 39.

The sum is 39.