Crazy Math Trick - Multiply up to 20 x 20 in your Head

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[bsgrn17]

rather do this for 15 and 13.

do 15 * 10 that is 150.

then do 15 * 3 that is 45

add them up and get 195

[TheBfamilly]

isnt it beter to multiply 15 by 10 and then by 3 you get 150+45.yey 195 :D

[fistrow89]

You make things harder to do.

[al4381]

i discovered that in seventh grade, i allways use that metod

[bennyt914]

And following that algebra, 20*20 will work for this method, as long as you realized that slashing the 1 off the front is actually a subtraction of 10. Instead of slashing the 2 off and using 0, use 10. You get 10(20+10) + (10*10) = 300 + 100 = 400. Though by and past this point, you will be using 2 digit multiplications to find your answer using this method, which is exactly what it seeks to avoid, so it becomes obsolete.

[bennyt914]

x = 15, y = 13

xy = 10 * (x + y - 10) + (x - 10)(y - 10) = 10x + 10y - 100 + xy - 10x - 10y + 100 = xy

It's just rearranging the algebra a bit to use easier numbers, no magic here.

And yes, to most people, (15*10) + (15*3) is easier, but that's just because most people can multiply 15 by 3 quickly. Whereas those same people may have more difficulty with say, doing 19*9 from the same method applied to 19*19. The video method makes the operations use only a single digit, besides the easy * 10.

[prettyvase]

wow! i never knew this. thanks

[ColdHeartedMan86]

@ohyshit the fun is it works also for +20 times -20 (above and below). 15*23 = (15+13 )*10 = 280 5*13=65 65+280= 345 but 5*13 is in this example easy, but could be more worse. Indeed is this was just usefull with nubers below 20 - but it holds for all numbers. (it's math it must be consitant) [sorry for bad english ...]

[sajiraghavan]

this is vedic math method, especially base multiplication. This is a specific case and we can do only calculation which are very close to the base. There are very good and amazing tricks that is applicable universally, i mean to any number of digits by any number of digits.

[arunramesh1]

wow it was so good i really like this , Thanks buddy u have opened my eyes which no school can do

[QuallBrall]

@filek1011 its a generell way...