Multiplication trick

You mean 25, 36, 49 etc?
Yes.

Obviously you can't memorise them all, but is makes mental arithmetic a lot easier if you just know a bunch of results without having to calculate them.

Squares are useful so worth memorising.

I understand, that might be the first step.

If you're interested in why that is, you should watch this excellent video

youtube.com/watch?v=UBVV8pch1dM

For know, your brain will follow instructions, but the next step is making it intuitive so that it costs less mental "stamina".

good vid user
i am trying to get highscore in brain age 3ds

(must play if someone is having problem concentrating)

this is a good way to solve small prob easily

For multiplying larger numbers in your head, here's what I do:

Find the nearest easy to work with number to each, like a multiple of a power of ten. Call these a and b.
Take the difference between those numbers and the originals, call these c and d. Then do this:

(a-c)(b-d) = ab - 2(ad + bc) + cd.

If you choose a and b well, this should be pretty simple. Also make sure to account for the signs of c and d.

Whoops, put a 2 in there because I usually use this for squaring things. Ignore the 2.

can you give a example ?

93 * 47 = 100*50 - 100*7 - 50*3 + 21
So 93 * 47 = 5000 - 700 - 150 + 21 = 4171.

another good trick user
took me some time to understand

93 *47 = 4371

(a-c)(b-d) = ab - ad + b + cd.

using a calculator

Ah, you got me there. In my defense, I haven't slept in about 2.5 days, not that that matters.

It should be

93*47 = 100*50 - 100*3 - 50*7 + 21
93*47 = 5000 - 300 - 350 + 21 = 4371.

When I was younger I always had trouble meme-orizing the "late mid" tables, i.e. 6*7, 7*8, and hell, even the additions, 6+7, 7+8. I just had to grind that out. One way I tried to help remember was for instance for 7*8, get 6*8, 48, and add 8, 56.

go get a good sleep
knowledge without sleep not worth it

(a-c)(b-d) = ab - ad + b + cd was also incorrect
correct is

irrelevant to the topic but is this correct:√245 = √49*5 = 5√7
i understand the concept but i can't figure out an easy way to figure out the middle part

I don't remember ever memorizing these, yet I have them completely ingrained into my brain.

As said, similar to a language.

91*44 = 100*50 - 100*9 - 50*6 +54
91*44 = 5000 - 900 - 30 +54
91*44 = 4124
but
91*44 = 4004

what am i doing wrong

you did too much math and now you can understand things others cant
just like musicians can tell which note is being played just by hearing

idk how it works on maths

Same thing I did. Multiply the new numbers by the difference between the other pair. In your example it would be:

91*44 = 100*50 - 100*6 - 50*9 + 54

that solved it

are you...black ?

indian
i guess its the same thing

Oh, another good trick I sometimes use involves the classic "multiply by nine using your fingers" trick. If you want to find a*b, you can pretend you have a+1 fingers, imagine bending down the bth one from the left, then set the number remaining to the left and right as your first and second digits. Then you just convert to base 10 and you're done.

Note that this requires you to choose a to be the larger of the two numbers.

70/3.6 = 70/(36/10) = 70/(18/5) = 70/18*5 = 70/2/3/3*5 = 35/3/3*5 = (36-1)/3/3*5 = (12-1/3)/3*5 = (4-1/9)*5 = 20-5/9 = 19.444...

2*2*2**2*2*2
7**2*2*2
^that number minus 7

So long as you know 8 is 2*2*2, its easy. Idk any other way to avoid memorization because math is entirely memorization.

When exactly did you have to "grind that out" this is shit Americans know by heart by age 10