>>21008038>anon if you were capable of performing the calculations in your head, they still wanted you to waste the time working it out exactly how they showed it on the chalkboard.necessary in a testing environment, otherwise children will try to put numbers together using make-believe rules that only work sometimes, and result in errors the kids will be unable to stop making for the rest of their lives
> you can get a good estimate of the solution to a multiplication by just putting the first numbers side by side> for example, multiply 9 times 99 and the result is pretty close to 999> and so 2 × 5 is pretty close to 25except the actual answer is closer to 0 than your "estimate," which makes it not an estimate at all
