Its very easy to multiply any two digit number by eleven once you know the secret. Consider the following problem.
12 x 11
To solve this simple add the digits, 1+2 = 3, put the 3 between 1 and 2, and there is your answer:
Consider another problem:
35 x 11
Since 3+5=8, your answer is simply
Now do this in you mind.
45 x 11
Now let us move to a bit complex problem. Suppose the problem is
76 x 11
Although 7+6 = 13, the answer is NOT 7136!
As before, the 3 goes in between the numbers, but the 1 needs to be added to the 7 to get the correct answer i.e 1 will be moved as carry to the next digit. So the answer will be
88 x 11
will give ans
Take a moment to practice this skill a few times. You have to practice these tricks otherwise you will forget them very soon. Whenever you find some free time take a pen and a paper and make problems by your own and solve them. This first lesson is much easier while the problems will become complex after a few days so for that you need practice. The more you will practice the better you will be at mental calculations.
The answer to the problem 45 x 11 is 495.