How to multipliy faster using the speed math technique

Look and read carefully now i am going to teach you the speed math technique of multiplication.

Firstly you must know normal multiplication so I will tell you what is multiplication in a simple way
it is basically repeated addition like for example

6+6+6+6+6=30 so even 6 x 5 = 30

Now for the speed math technique, for this technique you dont need to know tables at all you can just calculate it in your mind so first take a paper and choose any two numbers suppose take 7x8 and draw 2 circles below the numbers like this

                       7      x      6
                      O               O

Then subtract 10 minus seven =   3 and 10 minus 6 is = to 4 , write  -3 in the circle below seven and -4 in the circle below six . Now subtract crossways even if you do 7-4 or 6-3 you will get the same answer that is 3 so write 3 like this

                      7        x      6 = 3
                     -3              -4     

Now add a 0 to 3  so you will get thirty and multiply 3 and 4 at the bottom so now you have 30 and 12 respectively. At last all you need to do is add 30 and 12 so 42 is the answer.