Question

What other compatible numbers could you use for 428 and 286

Answer 1

How about raising 286 up by 14 to 300 and compensating by lowering 428 by the same 14 Since I know that 14 + 14 is 28  then 28-14 is 14
So 428 - 14 = 414
So now I have 414 + 300 which I can do mentally - the answer is 714 and is also the answer to the original problem 428 + 286

Compensation works very well - bring one number up or down to a rounded number and compensate by doing the opposite to the other  - instead of 199 + 457 - try 200 + 456
Same answer and because one of the numbers is nicely rounded, it is easy to add the other. 

One more:  207 + 182  becomes 200 + 189 =389   I lowered one by 7 and raised the other one by the same 7.