3 ms·
I do it quite differently, because I am good at operations, but I have a bad memory. 37 x 110 -> 4070 (mentally I visualize 3700+370 . This is not fully obvious
by reacweb 9y ago
I do it quite differently, because I am good at operations, but I have a bad memory. 37 x 110 -> 4070 (mentally I visualize 3700+370 . This is not fully obvious because of the carry), then I try to remember this number so that I can add 185 (when I see 37x5, I see 18.5x10 without other intermediate step) to it and remember the result.
The "normal" way is 30 x 115 -> 3450 (easy because I can see 3x15->45, so it is as if there was no carry), then 7 x 115 -> 805 (not obvious because of 2 carries), then I have forgotten the 3450, I recompute it while trying to remember 805.
For me, the aim of all these tricks is to cope with a bad memory.
- reacweb 9y agoI also likes the table of 37, but this works better for smaller numbers. This gives: 37 x 115 -> 37 x 3 + (114 / 3) + 37. I know that 37x3=111. With some efforts, I can see that 114 / 3 -> 38. I am still memory free to perform the difficult 111x38 -> 3800+380+38 = 4180+38 = 4218 that I pain to remember to add 37. In this case, the table of 37 is not very effective.