Vivly:
.
I think this only works when the sum of the two digits is less than 10.
For example 67 * 11 isn't 6137.
It's 737. I stand to be corrected though.

Maybe it's the normal addition to the LHS of Tens, Hundreds e.t.c.

I.e.
67 * 11
6 « [6+7] « 7
[6+1] « 3 « 7
7«3«7 =>737

Also:
378 * 11
3 « [3+7] « [7+8] « 8
3 « [3+7+1] « 5 « 8
[3+1 ]« 1 « 5 « 8
4«1«5«8 => 4158

Educative posts like this hardly make front page

Dongreat:


You stand to be corrected for this and for the hack method it works for a limited numb of digits. It's mathematics dear, truth is there is no right method 2 get a precise ans as maths itself is not accurate but provide numbers next to something. These are short cut techniques that work with large amount of numbers but not all. like u said, limited.

Just seeing this.funny enough,when it comes to multiplying by 11,no one taught me any trick,I just stumbled on it smhw.I remember clearly in my js2 n 3,l always played with my calculator ,manipulating numbers during my spare time n that was he I notice d relationship firstly with 121,132,143,154,165 n so I worked on it 4 higher numbers n saw d need to add when d sum is greater than 10.nice post @op