Hi Everyone,
The swelling in my fingers from my post on Sunday finally went away and I can type again.
Getting back to that riddle with the teacher- when I was in 10th grade we were learning ???? ????? and in ??? ?? the end of second Mishna says ?????? ???? ?? ???????, ????? ???? ?? ??????–???? ???? ?? ????? ??????; ??? ????, ???? ????? ?? ??????? ???? ??? ?????. So our Rebbe asked us to add up the total amount of 1 + 2 + 3 + … + 60.
The plan I came up with was to add the numbers 1 through 10 (I used a shortcut for this, I already knew from the boxes of Chanukah candles that Telze sends out that the sum of the integers of 2 through 9 is 44 and 44 + 1 + 10 = 55), the sum from 11 to 20 is just 100 more and from 21 to 30 is just 100 more than that. Continuing we have 55 + 155 + 255 + 355 + 455 + 555 = 50 + 150 + 250 + 350 + 450 + 550 + 6×5 = 1800 + 30 = 1830.
It’s not as fast as the other one I posted and is impractical for large numbers and numbers not ending in 0, but it does work.