30 second arithmetic challenge | Hacker News Reader

30 second arithmetic challenge

christianp.github.io

74 points31707040 comments

I was doing fine until I got to "multiply by itself twice". Is that "x := x * x * x", or "x := x * x; x := x * x"?

This caught me out too.

This reminds me of morning routine back in grade school called "Mad Minute" where we would be given a sheet containing 30 or 50 simple equations to solve. You'd have to complete it in a minute and the teacher would stopped grading at the first wrong answer so getting the first one wrong follwed by 49 correct answer would net you a score of zero.

When I first transferred to that school I was terrible at it but I did get pretty good at it later on. I think it did a lot for my arithmetic skills.

I hated "Mad Minute." I felt I had to do perfectly on it, since some other kids did - and that was the standard the teacher set.

Another fun game you can play in traffic[0] is to factor the license plates of the cars ahead of you.

Weirdly, I found that doing this sort of practice made me better at abstract mathematics. I used to think that Gauss, Euler and von Neumann being excellent mental calculators was a side effect of their talent, but I wonder now if this sort of practice actually amplified it instead.

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0. In your car-- on foot it's surprisingly dangerous.

That's surprising. Mathematicians generally are not very good at calculations and it always seemed to me that doing calculations fast is quite different from mathematicians do and need.

Back in the time of Gauss, mathematicians needed logarithm tables, and the only ones they trusted making them where mathematicians. So, mathematicians computed logarithms 'in their spare time'

For example, Gauss actually spent time to write a review of a table of logarithms (http://articles.adsabs.harvard.edu//full/1851AN.....32..181G...).

He also had to compute prime numbers so that he could study their properties. (http://science.larouchepac.com/gauss/ceres/InterimII/Arithme... claims he extended a table listing all primes up to 10,009 but never got as far as a million, but he must have spent lots of time on calculations we now call mundane

This is a myth. Mathematicians are excellent at calculations, relative to the general population. They know many algorithms and notice patterns (like "Common core"). They just aren't usually the savants that multiply many diot numbers.

Much of advanced mathematics does involved laborious calculations. They are just on more sophisticated domains than integer arithmetic.

Why is it more dangerous on foot than in your car? I'd have expected it to be the other way around.

I think the joke is that being on foot in [car] traffic is more dangerous than being in a car.

Yeah. There's a related XKCD[0], but let's just have an irony free moment of total seriousness for the following: be alert when walking places, getting hit by a car is extremely unpleasant.

0. https://xkcd.com/356/

I wrote a small script to solve the easy ones in the browser: https://github.com/rhnvrm/30s_challenge

Here is the script for solver: https://github.com/rhnvrm/30s_challenge/blob/master/solver.j...

and here is the cheat: https://github.com/rhnvrm/30s_challenge/blob/master/cheat.js

Also, I found that since the methods of the game and challenge class are public, you can actually just call it's functions. I also found a useful resource for learning OOPs in js http://phrogz.net/js/classes/OOPinJS.html and how to make methods private. There is another cool article here on how to make members private and protected here http://philipwalton.com/articles/implementing-private-and-pr...

This makes me realize my long multiplication above 100 really sucks.

Jeez, I got to like operation 3. That said, I am surrounded by beer cans, so... yeah, don't drink and derive.

I think hard is bugged? It is around easy's difficulty and much easier than medium.

Medium and hard throw in new kinds of operations, but how hard a problem is for me at least seems to mostly scale with the number of digits I have to juggle, not the operation "complexity".

E.g. if I'm at 14, an "easy" multiply "by itself" forces me to multiply long-form (I don't even have 4 x 14 in my mental LUT... so 140 + "uh... 56 plus..."). On the other hand, again starting at 14, a "hard" multiply by 4/7 instead is trivially 8 (mentally rewriting to (14/7)*4)

It is. I failed a few easier (ran out of time, or got wrong results), but complete hard ones without any issues.

Also, easy has stuff like "7x12", which is not-so-easy (you only usually memorize multiplication tables up to 10x10).

Hard, however, has things like "54/9", which is trivial and I could have done being 10 years old in an instant.

This reminds me of a math game we used to play in elementary school called 24. I also recreated it, uses websockets for multiplayer:

https://get24.jit.su

Please allow easy editing of previous wrong guess

Really fun, nice game!

4/6 easy, 19.1s 47/77 medium, 16.2s 19/25 hard, 17.8s

I started scribbling numbers on paper without looking down when I got to the hard ones, which helped...but I still think the hard ones were slightly easier than medium ones.

Good question design: forcing you to look ahead simplify things like 69 * 2 - 5 / 7 ...

realizing that 69 is one smaller away from being evenly divisible by 7, when doubled is 2 smaller, minus 5 makes it 7 smaller so the divided by 7 can apply to the thing it's close to...140 as well as the 7 smaller..140/7 minus 1...19

Common core on steroids?

Please make / and + more distinct!

Yes, it's hard to see the difference.

This is the most infuriating thing I've played since QWOP

Didn't know that one, lucky it's saturday

Looks like a place to practice mental arithmetic tricks, you know, like multiplication by 11:

  11 × 16 = 1(1+6)6
  34 × 11 = 3(3+4)4
  124 × 11 = 1(1+2)(2+4)4

Or multiplication table 10 through 20:

  14 × 17 = (14+7) × 10 + 7 × 4
  13 × 18 = (13+8) × 10 + 8 × 3

I don't understand how this works. Are you supposed to enter the answers as you go? Or just the final answer? I tried entering intermediate values and got zero feedback from the interface.

The trick seems to be to avoid subvocalising (where possible).

Subvocalising the operations or the current value after each step? I feel like the former would slow me down, but I found the latter important for keeping track and I was getting through them in a decent time.

Why does that help?

supposedly subvocalising is slowing you (resources allocated to your TTS module rather than to your arithmetic coprocessor ;)

This is the most infuriating thing I've played since qwop

This is a rather fun little exercise. Would be good to use in a classroom, although I found it a little hard going from left to right on a laptop screen

Small bug: When you did not solve it in time and the answer is diplayed, clicking on the timer will add it to the solved count.

11 ... ok

+5 ... easy

x itself ... ugh. more coffee.

divide by 7 ... TI83 slides out of desk drawer

Actually it's really fun - thanks :)

Fun, reminds me my school classroom exercise in elementary

Got an A in calc II but this gets the better of me? GRRR!

It's arithmetic, not calculus. In both your performance depends on three factors: technique, practice, capacity. I don't know about capacity, but practising and learning calculus techniques is not the same as practising and learning arithmetic techniques. In fact if you wan't to get good at calculus it is probably counter-productive and inneficient to waste time on solving arithmetic operations "by hand" when using a calculator will be much faster and help you keep focused on the calculus problem at hand.

Thanks. That made me feel a whole lot better about sucking at this. :-)

This is amazing, and I need to work on my arithmetic.

Its like kind of frappy bird game, some may get addicted, not to lose...

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