Suppose you have two numbers let them be 27 and 88. To add them quickly follow these steps.

numbers like 21 , 31 etc to be rounded off to nearest 10 and the additional part is surplus i.e we can write 21 as (20+1).

numbers like 28 38 etc also to be rounded off to nearest 10 and the remaining part is deficit i.e we can write 28 as (302).

now add the 10's terms together and 1's tern together i.e in case of 27 (303)and 88 (902) it will become 120 (10's) and 5(1's).

now see if total 1's is surplus or deficit. If it is surplus add 1's to 10's and vice versa. In this case it is deficit so subtract it. hence 1205=115.
In short 27+88 can be written as (303)+(902) == (1205) => 115
Try to solve these using same trick.  19 + 78
 34 + 44
 55 + 67
 64+36
 88+76