This is a strategy you may use to make addition easier.
I call it "adding up to ten strategy", that requires to find any numbers that add up to 10.

Example: 
Find the sum of: 7 + 8 + 3 + 2 + 5 
7+3 is 10, 
8+2 is another 10, which makes 20, 
Plus 5 is 25
The total is 10+10+5 = 25
Easy!