I thought that too, 9 is like a halogen, it wants to resolve to 10 anyway it can like fluorine wants one last electron. So allow the 9 to rip one off of the neighboring numbers and then perform the calculation.
I’ve never really liked the anthropomorphic description of chemical bonding, but maybe it’s actually similar to the addition thing. On the one hand, we can say 9 wants to resolve to 10 and takes a 1, and on the other hand we could say there are a bunch of different ways we could rearrange these numbers but the end result is the same as if we resolve 9 to 10 first. Maybe chemical reactions are similar, so there’s a bunch of configurations that could have happened, but the end result is the same as if we had said fluorine wants that last electron
The second method is very chemistry-like. I do that too naturally
So do I! When I saw that 9 stealing a 1 and becoming a 10, I thought “Wait… These are electrons. This is chemistry. That 9 is a halogen!”
I thought that too, 9 is like a halogen, it wants to resolve to 10 anyway it can like fluorine wants one last electron. So allow the 9 to rip one off of the neighboring numbers and then perform the calculation.
I’ve never really liked the anthropomorphic description of chemical bonding, but maybe it’s actually similar to the addition thing. On the one hand, we can say 9 wants to resolve to 10 and takes a 1, and on the other hand we could say there are a bunch of different ways we could rearrange these numbers but the end result is the same as if we resolve 9 to 10 first. Maybe chemical reactions are similar, so there’s a bunch of configurations that could have happened, but the end result is the same as if we had said fluorine wants that last electron
Although, electron affinity is a thing… so the analogy does break down pretty quick. Rip