 Remember in the preceding video, when I had an interval that ended at 10.15 and began at 8.20? And I had to borrow before subtracting to get 1 hour and 55 minutes, which comes out to 115 minutes total. While I was setting up that previous video, I had another thought. This is the way I did things in grade school, but in grade school we didn't understand negative numbers. What would happen if I were to use negative numbers? Let's end at 10.15 and begin at 8.20. And this time, do the subtraction, that's 2 hours and negative 5 minutes. Instead of being scared of negative numbers, let's go with it and see where it leads us. That's 2 times 60 is 120 plus negative 5, and I still come out with the correct answer of 115 minutes. It turns out that having to do the conversion to minutes past midnight, while it was a good technique, and it avoided doing any borrowing, was something I didn't need to do. The lesson to be learned is a good first start is to do things the way you learned it originally by hand, but you don't have to be tied down to it. If you try a different method, you may find something that's even better.