I didn’t use this method as a kid, but I do use it or something like it pretty often to solve the math formula that my phone requires to turn its alarm off because that can go up to 15 and I don’t have above 10s 100% well memorized. I can get 10, 5, 1, and 2 of anything pretty quickly, so 11 is 10+1, 12 is 10+2, 13 is 10+5-2, etc. I don’t think it would have met the speed requirements of my times tables tests back in elementary school, especially because I was probably slower on my 2s, 5s, and addition back then, but 2-3 iterations is generally few enough that I can close the alarm before it gets too loud/annoying, even in a half-asleep state
I didn’t use this method as a kid, but I do use it or something like it pretty often to solve the math formula that my phone requires to turn its alarm off because that can go up to 15 and I don’t have above 10s 100% well memorized. I can get 10, 5, 1, and 2 of anything pretty quickly, so 11 is 10+1, 12 is 10+2, 13 is 10+5-2, etc. I don’t think it would have met the speed requirements of my times tables tests back in elementary school, especially because I was probably slower on my 2s, 5s, and addition back then, but 2-3 iterations is generally few enough that I can close the alarm before it gets too loud/annoying, even in a half-asleep state