Common core is easy af because it's closer to the way the human brain actually thinks about numbers.
5,327+860=6,187 because... well, we added every single 1 together and thats what came out.
Vs.
5,300+850+30-3+10
Got a chunk of about 5300, got a chunk of about 850. Stick the chunks together. Ok, now we've got a chunk of about 30, and a chunk of 10. Stick them all in the mix. All right, so getting more specific, that chunk of about 30 was three short, so lets take that away. Wham, answer right there.