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.
