Math Tricks, multiply by 20's

I have posted how to calculate from 11-19 by 11-19 within few minutes, but now I would like to share how to calculate 20-29 by 20-29. It’s also simple like calculating like before but there is slight change in the formula. In the previous one you have to multiply the last digit by 10, which as over here you have to multiply the last digit by 20. Anyway let’s get through the process so that you would easily learn it.
Let’s calcue 27*29.
In this process, what you have to do is add 27+ last digit of the another number (9), it would become 36, then multiply that number by 20, which will become 720.
As a second step multiply two last digits of your number (i.e. 7 and 9) from your digit, it will become 63. Now add up your two sums (63+720), it would become 783. That is your answer for your multiplication. Isn’t it easy to calculate in your mind within few seconds. Try some of the multiplication by yourself and show your capacity to your friends, they will be happy with your ability.