Is guessing your answer to solve your problem.
like 128+1393= My guess (estimation) is 1620.
Doesn't matter if your estimation is wrong, that the point of estimating
Rounding is rounding your number to the closes tens,hundreds, thousands and etc...
Example like for tens.
34 = 30
645 = 650
Same goes for hundreds.
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
Rounding--> (30+40)=60 <-- (Guessing the answers to your problem.)
Now just add the left over.
Now you have your answer.