Why does the calculator trick work?

The one that goes: Key in the first three digits of your phone number (NOT the area code) Multiply by 80 Add 1 Multiply by 250 Add the last 4 digits of your phone number Add the last 4 digits of your phone number again Subtract 250 Divide number by 2 Is there some mathematical explanation to that? If so,... show more The one that goes:
Key in the first three digits of your phone number (NOT the area code)
Multiply by 80
Add 1
Multiply by 250
Add the last 4 digits of your phone number
Add the last 4 digits of your phone number again
Subtract 250
Divide number by 2

Is there some mathematical explanation to that? If so, what?
3 answers 3