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

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. 

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