How to add and subtract quickly - Trick to add and subtract easily

  HOW TO ADD QUICKLY  The easiest way to add and subtract quickly is doing an approximation of one of the numbers. 

Let's imagine we have the following addition: 

Now, we can see that both are possible to be approximated. You can add to one of numbers to make the easier to add. In this case, we will add 7 to 23.

Now we have 1589 + 30. 

Let's do the addition.  

We have as temporal result the number 1619. But now is necessary subtract the quantity we add. So, 1619-7 = 1612. This is the final result.