Here is a very nifty or cool way to multiply by 11.
It is so simple and believe it or not, even easier
than doing it on a calculator!

The rule is very simple: To multiply a
two-digit number by 11,
just add the two digits and place the sum
between the two digits.

For example, suppose
you need to multiply 45 by 11. According to
the rule, add 4 and 5 and place it between the
4 and 5 to get 495. It’s as simple as that.

The above way is only applicable if the sum
of two-digit number is less than 9. If the sum
of the two digits is greater than 9, then we
place the units digit between the two digits
of the number being multiplied by 11 and
“carry” the tens digit to be added to the
tens digit of the multiplicand.

Let’s try it with 78 x 11. Since, 7 + 8 = 15,
we place the 5 between the 7 and 8 and
add the 1 to the 7, to get [7 + 1][5][8] or 858.

note: for number 50;
0 is the units digit
5 is the tens digit

for 7 x 5
7 is the multiplicand
5 is the multiplier

This is only applicable for two-digit number...

ok ah..galing!!