ArithmeticfilterJanuary 26, 2015 8:41 AM   Subscribe

Nothing but an endless supply of mental arithmetic problems. Five levels of difficulty, from "10 - 6" to "√370881."

You can find slightly more granular training here. See Wikipedia for a survey of mental methods, or read A.C. Aitken's explanation of his Art of Calculation.
posted by Iridic (20 comments total) 20 users marked this as a favorite

I can see how to get on the bike but getting off is not so easy.
posted by biffa at 9:03 AM on January 26, 2015 [1 favorite]

Why would I want to do simple maths under pressure?
posted by thelonius at 9:09 AM on January 26, 2015 [1 favorite]

√370881:
1, 600^2?
2. >600
3. >600 + (370881-360000)/2/600
4. >608.35
5. Calculator Check: 608.35^2=370089.7225
6. Calculator Check: √370881=609
7. D'oh! the end "81" should have been a clue to me.
8. Still, not bad.

Yep, I'm the fish this site is trolling for.
posted by IAmBroom at 9:13 AM on January 26, 2015 [7 favorites]

608.35 is within the margin of experimental error!
posted by thelonius at 9:21 AM on January 26, 2015 [1 favorite]

Can I nope?
posted by colie at 10:04 AM on January 26, 2015 [1 favorite]

I once got an alarm on my phone that required you to answer a math question correctly before it would turn off. I thought this would be great, and assure I was actually awake. Also, thinking I'm hot shit at math, I put it on its hardest setting.

It turns out that at 7am, having just woken up, with your alarm is getting progressively louder and your wife yelling "why is that happening?! make it stop!" you realize that pulling the battery out of your phone is still faster than solving 48*37-442 in your head.

math under pressure indeed.
posted by jermsplan at 10:29 AM on January 26, 2015 [9 favorites]

I figured out the first one: 10-6= ? (If anybody needs help.)
posted by LeLiLo at 10:34 AM on January 26, 2015 [4 favorites]

Also: You Can't Do Simple Maths Under Pressure.

Oddly, I am better at doing simple maths than reliably associating my left hand with the button on the left side of the screen. I guess it's sort of like how the Watson on Jeopardy experiment proved that at the top levels the most important thing was who had better button-pushing discipline.
posted by benito.strauss at 10:35 AM on January 26, 2015

√370881:
1, 600^2 = 360000
2. (600+x)^2 = 360000+2*600*x + x^2
3. 1200x +x^2 = 10881
4. 1200*10=12000. x <10
5. 9^2 = 81; 1200*9=10800; x=9
6. 609

On the hook.
posted by Four Ds at 12:36 PM on January 26, 2015 [1 favorite]

I primed it out to 609, starting with 3*3*7*7*29*29.
posted by Oyéah at 1:13 PM on January 26, 2015 [2 favorites]

There's gotta be way I can make this interesting for my nine year old... So much cooler than anything else he can play on a phone...
posted by From Bklyn at 2:10 PM on January 26, 2015

colie: "Can I nope?"

Sure you can nope, but only if you can't yep.
posted by symbioid at 3:22 PM on January 26, 2015 [1 favorite]

Pfft - genius is easy - adding long strings, since nothing prohibits you from typing left<-right, then just add like normal. Now if time were involved or more complex math, then, yeah... I'll keep going until I see something that's not just a long string of stuff.
posted by symbioid at 3:25 PM on January 26, 2015

posted by clvrmnky at 3:49 PM on January 26, 2015

OK -got a non-add one...

I was close:
2746200 ÷ 29850 = 92
You incorrectly answered: 93
posted by symbioid at 5:19 PM on January 26, 2015

√370881:
1. Obviously ends in 9.
2. Gonna be a bit over 600 since 600^2=36000.
3. So maybe 609?

[Two time state champion in Number Sense >30 years ago.]
posted by neuron at 10:20 PM on January 26, 2015

neuron: √370881:
1. Obviously ends in 9.
You cheated by assuming an integer.
posted by IAmBroom at 9:33 AM on January 27, 2015

That, my friends, is a pretty good encapsulation of the difference between a mathematician and a physicist.

(As someone falling on the math end of that spectrum, I'll point out that if the answer is not an integer, it would be impossible to give a correct answer in decimal notation. I expect that to non-math types this observation is technically true and practically infuriating.)
posted by benito.strauss at 3:47 PM on January 27, 2015 [1 favorite]

Heh... I'm an engineer who is required to use two decimal places on his current project - most require three, so a lot of drawings are filled with numbers ending in "0".

:)
posted by IAmBroom at 9:38 AM on January 28, 2015 [1 favorite]

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