The trick to left-to-right subtraction is to write down the resulting difference right away, then "slash" through it to borrow from it. When I was designing my

The trick to left-to-right subtraction is to write down the resulting difference right away, then "slash" through it to borrow from it. When I was designing my custom flashcard program, I played with around with different input methods because that became the bottleneck: You can actually spit out the answer faster than someone can enter the digits into a calculator! (as someone else reads off the problem)