Maths Problem

138 + 349 = 487

You can use this strategy in your maths:  
100 + 300 = 400
30 + 40 = 70
8 + 9 = 17
400 + 70 + 17 = 487

So how I worked this problem 
first did 100 + 300 = 400
then i did 30 + 40 and that = 
to 70 next I did 8 + 9 that = to 17
so i add them all up and I got my
to answer to 487.