[thoughtomator]

First 3 digits = X; last 4 = Y
Phone number = 10,000X + Y

(250*(80X+1) + 2Y - 250)/2 is then the expression of the steps indicated.

So our equation is
(250(80X+1)+ 2Y -250)/2 = 10,000X +Y

factoring this out brings us to
(20,000X + 250 + 2Y -250)/2 = 10,000X +Y

drop the 250s as they cancel each other out, and do the division:

10,000X + Y = 10,000X + Y


(I learned to do this math in 4th grade, if I remember correctly)

[PetroniDE]

Took Freepers about 5 minutes (add three to typing response) to figure this out.

Post this on DU. Let's see how long it takes them to figure it out.