I misread the title of this at first as "How to quickly multiply numbers by 10 and 20"

I was like "people need a trick for this????"

*quality braining! Certainly blew my mind.

Boosting this quality contribution up in the Hot Listing - declared quality by gwiz665.

It's pretty neat, but too slow. I can do it faster in my head than on paper like that.

I use a trick that I don't know a name for.

Multiply by factors of 10 first. Ex. 18X12 = 18X10 + 18X2 = 180+36 = 216

I've relied on it for years and it comes naturally by now. I can calculate the products of any 2 digit numbers faster than anyone on paper.

Yeah that's what I do as well but this way seems quicker.

This is dumb.. it doesn't work outside of 10 to 20??!!

18 x 12 = 10*10 + 8*10 + 2*10 + 8*2

see why this 18+2=200 part works??? (then add in 8*2)

(10 + * (10 + 2) = FOIL...
that is all he is doing, but he is combining three operations as add 18+2

This works with all numbers, but in his way only works for 10 to 20 because of the 10 and 10 leading factors.

Yeah that's the method he talked about in the first half of the video. I think his method is faster (but maybe only if the sum and product of last digits are less than 10), you're not meant to do it on paper he just did it like that for demonstration purposes.>> ^Throbbin:

It's pretty neat, but too slow. I can do it faster in my head than on paper like that.
I use a trick that I don't know a name for.
Multiply by factors of 10 first. Ex. 18X12 = 18X10 + 18X2 = 180+36 = 216
I've relied on it for years and it comes naturally by now. I can calculate the products of any 2 digit numbers faster than anyone on paper.

The highlight for me was the use of the word "maths" at the end, instead of "math".

>> ^Throbbin:

It's pretty neat, but too slow. I can do it faster in my head than on paper like that.
I use a trick that I don't know a name for.
Multiply by factors of 10 first. Ex. 18X12 = 18X10 + 18X2 = 180+36 = 216
I've relied on it for years and it comes naturally by now. I can calculate the products of any 2 digit numbers faster than anyone on paper.


Dunno why you'd be doing it on paper but this is computationally faster than our method, isn't it?

Add one digit to the other number, then a quick single digit addition. Whereas you're doing two multiplications (you might also need to break down the 2nd multiplication into further multiplications), then adding the two.

I use that same method you do, but this is clearly better for 10-20.

I may be a slave to tradition, but because I'm so used to the method we use I just find it faster, especially with numbers between 10-20 because it only requires multiples of 10 (and not the additional step of multiplying the multiples of 10 by other number that are required with anything over 20).>> ^dannym3141:

>> ^Throbbin:
It's pretty neat, but too slow. I can do it faster in my head than on paper like that.
I use a trick that I don't know a name for.
Multiply by factors of 10 first. Ex. 18X12 = 18X10 + 18X2 = 180+36 = 216
I've relied on it for years and it comes naturally by now. I can calculate the products of any 2 digit numbers faster than anyone on paper.

Dunno why you'd be doing it on paper but this is computationally faster than our method, isn't it?
Add one digit to the other number, then a quick single digit addition. Whereas you're doing two multiplications (you might also need to break down the 2nd multiplication into further multiplications), then adding the two.
I use that same method you do, but this is clearly better for 10-20.

>> ^Throbbin:

I may be a slave to tradition, but because I'm so used to the method we use I just find it faster, especially with numbers between 10-20 because it only requires multiples of 10 (and not the additional step of multiplying the multiples of 10 by other number that are required with anything over 20).

Familiarity, yeah. But if you get familiar with this, it's easier still.

To use your example, I find this new way easier just because it's faster for me to add 200 to 16 than 180 to 36.

>> ^Throbbin:

It's pretty neat, but too slow. I can do it faster in my head than on paper like that.
I use a trick that I don't know a name for.
Multiply by factors of 10 first. Ex. 18X12 = 18X10 + 18X2 = 180+36 = 216
I've relied on it for years and it comes naturally by now. I can calculate the products of any 2 digit numbers faster than anyone on paper.