Answer :

surekha
820. there  is a shortcut which can be used when adding consecutive numbers regardless of how big it is. it can also be done manually though
Trim
Simply it as follows:

1 + 39 = 40
2 + 38 = 40 etc

18 + 22 = 40
19 + 21 = 40

There are 19 of these plus 40 itself . . .therefore 20 of them

20 x 40 = 800

And finally the last number not used, 20

Therefore 800 + 20 = 820