4 ms·
I always wanted to make a custom arithmetic trainer that taught left-to-right arithmetic. Left to right arithmetic is faster (you can start reading the final an
by Leftium 2y ago
I always wanted to make a custom arithmetic trainer that taught left-to-right arithmetic. Left to right arithmetic is faster (you can start reading the final answer before you finish the less significant digits) and you get the most important information first.
The book I learned it from started by teaching that sums over 9 are "dot"-digit (so 7+8 = dot 5). When summing a column of digits, you just mark a dot so you don't have to hold a value larger than 9 in your head.
- rahimnathwani 2y agoyou can start reading the final answer before you finish the less significant digits Can you say more about this? Don't you always have to be prepared to change even the first digit? Like if you're adding 445 and 454, the first digit is 8. But, if just one of the last digits is increased by one, the first digit is 9. I know this sort of technique is useful for estimating, but it sounds like you were talking about something exact?
- Leftium 2y agoSo on paper: you write down 8 right away, and add an underline each time the next column results in a carry. When doing mental math on-the-fly: the carries may chain all the way back to the least significant digit, but most of the time you only need to look ahead one or two columns.
- rahimnathwani 2y agoI love it!
- Leftium 2y agoThe 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)