how does i know the actual Number, by which i multiply 8 and the answer come 80 . it is 10. but , What is the procedure if any one knows then please tell me.

I'm not quite sure I understand ur question...

 I think u meant:

     8*x=80

If so when u multiply any one-digit number by 10 you just add a zero to the end...

What is the opposite of "multiply"? Of course, it is "divide". So, you would divide 80/8=10. Example:

2 X 3=6. If you are given 2 and 6, how do you get 3 from 6 and 2? You, of course divide 6/2=3. And your problem is exactly the same.