When multiplying 2 digit number by 11

[jarlmeagher]

Hey Everyone,

My first post here. Just started studying for the GMAT and am finding this site very useful.

Wanted to share with you all a tiny trick that I learned today that's very simple.
It might be common knowledge, but I just heard about it. Goes like this:

When multiplying a two digit number by 11 you can add the values of the two digit number together and insert that value between the two digits for the answer.
43 x 11 =

[4+3] = 7

4 [insert value] 3 = 473

Looks like it only works when the combined values are less than 10 though.

[RumpelThickSkin]

did not know this .. this was helpful thanks a lot

[sakali]

Cool trick. Had not heard of it.

Still works for numbers where the sum of the digits is greater than 10.

For example: 64
6 + 4 = 10
Keep the zero and carry the one, so it works out to: 704