Hello,
1.*1.
This has nothing to do with extraordinary technique, but you gotta think about it (I'm confident that some of you know about it)..
So multiplying two such numbers is equivalent to :
 sum one of the numbers with the unit digit of the other one
 multiply it by 10
 add the product of the two unit digits.




I hope this would help at least one person in the future
Enjoy calculations !