Why didn’t we tak
e the whole number and not just the first 3 digit
We care about the difference between the “second chunk of 3 numbers” with the “first chunk of three numbers” and want the difference to be exactly 13.
Our problem then boils down to finding how many 3 digit numbers exist such that after decreasing it by 13, it is still a 3 digit number.
As you might be able to see now, the “six digit” part of the question doesn’t have much relevance.
This makes sense. I was stuck with the 6 digit rather the focus should be on 3 digit. Now it makes sense to find the total number of intervals in these ranges.