My niece asked me to help her with a problem, since she and her parents couldn't figure it out.
The question was: abcde - fghi = 42137
with a-i being 1-9 (so for example 12345 - 6789), with each digit appearing once.
I had no idea how to do this intelligently, and wrote some code which brute-forced through all permutations of 1-9 and give me the results ((43726, 1589),(43789, 1652),(47326, 5189),(47398, 5261)).
How would I go about this as a 9 year old student who cannot code this? Just trial and error? All we could really say is that the first digit is a 4 or 5, but thats it, aside from that it was just trying, and at some point I was so pissed with that task I wrote code to deal with it.