Estimating/Rounding

Estimating
 Is guessing your answer to solve your problem.
 

   Example:
        like 128+1393= My guess (estimation) is 1620.
 
 Doesn't matter if your estimation is wrong, that the point of estimating

Rounding

Rounding is rounding your number to the closes tens,hundreds, thousands and etc...
  Example like for tens.
 34 = 30
645 = 650
1254=1250

Same goes for hundreds.
1308= 1300
1459=1500
And it goes on and on.

Rounding and Estimating
Round and Estimating is just the same but they combine.  Let's say our question is

25+43=___
Rounding-->  (30+40)=60 <-- (Guessing the answers to your problem.)
Now just add the left over.
    5+3=8
    60+8= 68.

Now you have your answer.