Math trick for people who suck at multiplying

[Eternity]

So I love doing math equations ON PAPER. They are fun but if you don't know how to do basic math they can get annoying fast.

Good teacher = mind blowing
Anyways here is a cool trick, idk if everyone knows it.

[[MPGH]Wyo]

You need math so you can join the scammers in call centers to scam more?

[Wisel]

Already knew that, but unless taught in school I doubt many people will use that

[Dynamite]

I've seen this many times but never been bothered to learn it. Would be useful to have school.

[[MPGH]Mayion]

14 x 3 is 30 + 12
Just divide up your number and multiply the easy ones. Thats how i do it

[Danny]

personally find the standard portioning quicker. so 15x13 you break it down to (10x13)+(5x13). or 18x13 broken down to (20x13)-(2x13)

still, an interesting method that I remember being brought up as an option

[CzechOne]

just count with ur fingers

nerd

[Ferris Bueller]

I just use a calculator lmao but I don't understand why he doesn't show the proof on why this works. His method only works when you're multiplying 2-digit and below numbers together i think since he's using 10^1 as his base, which is already easy enough to do on paper. Anyways, this is base expansion multiplication and it's the basis for any kind of multiplication/addition/division you do:

14*12

The base 10 expansion for 14 and 12 is:
14 = (10^0)4 + (10^1)1
12 = (10^0)2 + (10^1)1

multiplying you get:
[(10^0)4 + (10^1)1] * [(10^0)2 + (10^1)1]
now you just distribute and you get:
[(10^0)4 * (10^0)2 + (10^0)4 * (10^1)1 + (10^1)1 * (10^0)2 + (10^1)1 * (10^1)1]

this gets you : 8 + 40 + 20 + 100 = 168 = 12*14

Now this looks a little complicated but it is essentially what we do when we do the normal hand multiplication method and the method he showed you and any other method that exists. This why when we multiply 2 digit numbers or 3 digit numbers, we add a 0 and then 00 to the result in the hand-multiplication method. We work in base-10 because we have 10 fingers so we don't really have to do base expansion to multiply or add it just comes naturally , but when you want to work in a different base, let's say binary, you need base expansion to convert back and forth.

[mincy1k]

You sir, have thought me more than my teacher