Multiply two Number when their unit digit Sum is 10 and 10th digit is Same

 

 For Exp.  15*15=   2[(1+1)*1]               25  (5*5)=225
          
Step 1. Just write unit digit multiplication result as 5*5=25 here on the right.
Step 2. Now add 1 to any 10th digit and multiply with other 
Step 3. Place it on the left of previous result.


     Exp2.   37*33=   4*3=12                  21  == 1221