Why they never just buy a calculator, I'll just never know...
RiderFan said:
Or using a pen and paper to work the problems out.
they are dealing with customers that are waiting in line; you'd probably want to do the math quickly in your head (and considering how popular Mizuki's group is, the line can stretch to a few dozen people)
It's less being a math whiz and more a skill that needs to be learned and developed. For those with this skill, simple math like this is way more quickly done in headspace than on calculator/paper.
For those who haven't developed this skill, then yes, a calculator would be the best. At least they don't need to add up prices like 496 yen or US sales taxes. Throw a bunch of that in, and I'd probably reach for a calculator. Or an abacus if you're oddly skilled with that like my grandfather.
Here's the mathie answer for you: 800x + 600y + 500z, x,y,z ∈ ℕ⁰. This is the set of every possible value, and so is infinitely more useful and interesting than a specific value.
Lesson: Do not ask mathies to do simple arithmetic. Mathies tend to be notoriously out of practice at the later, seldom having to go as far as getting an actual number. Ask someone from engineering or accounting instead... mathies do the abstract, not the practical.
The abacus is also a skill that can be learned and developed. For simple sums and multiplication like you'd need here, it doesn't take a lot of practice to get as fast as a calculator (or faster). Things like cubic roots take a lot of practice to get fast at (but are good practice in general because they involve a lot of smaller operations). The big difference between abacus and doing math in your head as a skill tends to be that abacus doesn't involve any knowledge of numbers or even thinking about the numbers... it's rote action. Someone tells you to "add 800", and unconsciously you either do the actions for "+5+3" or "+10-2" in the right columns depending on the beads you feel there. Which makes it very much like using a calculator once you're practiced enough.
I really feel like I ought to learn how to use an abacus and a sliderule. I don't expect to ever need the skills myself, but they seem like skills that ought to be preserved within the cultural consciousness just in case.
Here's the mathie answer for you: 800x + 600y + 500z, x,y,z ∈ ℕ⁰. This is the set of every possible value, and so is infinitely more useful and interesting than a specific value.
Well, every possible value in the set of natural numbers (including 0).
Mathies tend to be a bit nitpicky about stuff like this.
Lesson: Do not ask mathies to do simple arithmetic. Mathies tend to be notoriously out of practice at the later, seldom having to go as far as getting an actual number. Ask someone from engineering or accounting instead... mathies do the abstract, not the practical.
Would this include Number Theorists? Or would they be the odd exception to the rule? Either way, I can definitely see it, even in non-mathematicians that still study a lot of math, and even in myself at times (though judging myself for being slow at cubing two-digit numbers may or may not be a good standard).
Adding in your head is basically learning a bunch of shortcuts. In this case, 800 + 600 + 500, you take out the zeros and think 8 + 6 + 5. Then you add 6 + 5, which is pretty easy, to get 11, then you do 11 + 8 which again is a very simple sum. Other tricks, like decomposing numbers into well-known operations (3 + 8 = 3 + 7 + 1 = 11; 7 * 9 = 7 * 8 + 7 = 56 + 7 = 50 + 6 + 7 = 50 + 13 = 63) or shuffling units around (12 + 5 = 10 + 7 = 17), can help a lot. What tricks work best depends a lot on which operations you remember best, so it's a matter of constant practice. The biggest problem is keeping track of all the numbers, which can be remedied by starting the calculation right after you hear the first two numbers and keep a running tally. Again, practice practice practice.
Huh?ThngShss
ShssWhat's 800 plus 600 plus 500?That's right, but we'll manage on our own after this.Uh...lemme see...O-...one thousand, nine...hunnert?Think I maybe could lend a hand?
