Superb Math

Here is a math trick so unbelievable that it will stump you.
Personally I would like to know who came up with this. It is Pretty Amazing. Lemme know the logic behind.. if u can figure it out.......
1. Grab a calculator. (you won't be able to do this one in your head)
2. Key in the first six digits of your mobile number (India mobile No only)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your phone number (Not the total of 4 digits.)
7. Add the last 4 digits of your phone number again. (Not the total of 4 digits.)
8. Subtract 250
9. Divide number by 2
Do you recognize the answer?