How to improve mental arithmetic

[QNFan]

Out of curiosity, are you guys just naturally good at mental arithmetic?

How do you go about getting better, particularly with multiplication and division?

Thanks!

 

[Daniel Duffy]

Why do you want to do mental rithmetic?

 

[Jedison]

I've got these sorts of questions in trading interviews. I'm sure there are many ways to do them quickly. For multiplication I do them as: 42^2=(40^2+2*(40*2)+2^2) and division like: 250/7=(30*7+5*7+5)=30+5+5/7. Dunno if that helps

 

[tfors]

https://www.edx.org/course/mitx/mitx-6-sfmx-street-fighting-math-1501#.UzrcfqIarrs
this course has some mental calculation application.

 

[Daniel Duffy]

I've got these sorts of questions in trading interviews. I'm sure there are many ways to do them quickly. For multiplication I do them as: 42^2=(40^2+2*(40*2)+2^2) and division like: 250/7=(30*7+5*7+5)=30+5+5/7. Dunno if that helps

Another good one is compute exp(5) with pen and paper! asap

http://www.wilmott.com/messageview.cfm?catid=26&threadid=79451&FTVAR_MSGDBTABLE=

 

[Jedison]

I'd go with the power series representation

 

[Daniel Duffy]

I'd go with the power series representation

It will take you a lifetime

http://upload.wikimedia.org/math/0/b/c/0bc08045195dc823c22d1fa283cb0759.png

 

[Jedison]

haha true but n! grows pretty quickly, still maybe not the fastest. Whats e again...2.7 something

 

[Daniel Duffy]

haha true but n! grows pretty quickly, still maybe not the fastest. Whats e again...2.7 something

Up to 3! you should be OK; after that it's tricky.

 

[rajanS]

i heard the trachtenberg speed system is very effective for mental math.