50.82 + 39.38 = 50.80 + 39.40 = 50.20 + 40 = 90.20

50.82 + 39.38 = 89.82 + .38 = 90 + .20 = 90.20

I saw the original numbers as money. In the first solution I made friendly numbers, twice. In the second, I "put the big rocks in first."

I highly recommend introducing solving linear equations with bar models and here's why.