Question

What is the rounding or compatible numbers to estimate the sum of 198+727

Answer 1

Using rounding I would change 198 to 200 and 727 to 730.
200 + 730 = 930.  Some would change the 727 to 700 but I see no need to do that. My answer will be closer using 200+730.

You can also get the exact answer like this  - when you raise 198 to 200, you raised it by 2 so to compensate, take 2 away from the other number and 727 becomes 725
I can do 200 + 725 = 925 in my head and that happens to be the exact answer.