Becoming a human calculator

I was recently watching a ted talk where a guy is multiplying multi digits on the fly and basically just flexing on calculator peasants like me. I'm going to try and learn the skill set for my job to double check my work and also any future tests I take like the GMAT. Wondering if anyone on WSO has attempted the same and has any tips on where to start (Online lectures, Books, etc.....)

 

One time in college I memorized a bunch of random double digit multiplication problem sets (32 x 37, 73 x 89, etc.)... fast forward a few months at a super day for banking at a BB, and one of the hardo MDs asked me one of these double digit math questions .... well it was one of the problems I memorized and you should have seen his face when I answered it within three seconds.... ahhhh good times, failed the rest of the super day horribly though.

 

You don't have to memorize to get these in ~5 seconds. Here is my strategy that I would use for both of these

32(40) = 128(10) =1280

32*3 = 96

1280 - 100 + 4 = 1184

73(90) = (70+3)9(10) = (630+27)10 = 6570

6570-70 = 6500 - 3 = 6497

Array
 

While I agree with everyone that it is really pointless, it can be learned. A quick way to get started is to look at a digital clock and do permutations of every basic (add, subtract, multiply, divide) calculation possible with the digits. I do this to fall asleep and have since I was a kid.

“The three most harmful addictions are heroin, carbohydrates, and a monthly salary.” - Nassim Taleb
 

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