4 ms·
but that only works up to 10.. my method works for any number, and you could adapt it for x11... see below
by vaccinator 6y ago
but that only works up to 10.. my method works for any number, and you could adapt it for x11... see below
- alisonkisk 6y agoLucky for us, all digits are less than 10.
- vaccinator 6y agoWhat is 23 x 9 with that trick?
- cipherzero 6y agoJust going off the trick above would t it just be: 23 x 10 - 23 = 230 - 23 = 207... I guess I’m confused what point you’re making?
- vaccinator 6y agoI was talking about the grand-parent comment's method: > You can check you’re right if (a) the first digit of the result is 1 less than the number you started with The first digit of the result is 2 ... And the number that you started with is also 2, which is not 1 less... I guess I am not smarter then a 5th grader
- michaericalribo 6y agoWow! You definitely are smarter than me, the gp, at least! You’re right that my claim isn’t right in general. Hell, not even past 10, I can now see! I’m curious, how did you find that counterexample? I kind of ‘overfitted’ my mental model to the first 10 integers. But as a statistician I’m only in the business of being approximately right...! Nice catch. 23x9=207 starts with 20 which is 3 less than 23... 24x9=216, and 21 is 3 less than 24. 11x9=99 and 9 is 2 less than 11, 12x9=108 and 10 is 2 less than 12. So 0-9 are offset by 1, 10-19 are offset by 2, 20-29 offset by 3, 30-49 offset by 4?