This puzzle takes some twists and turns to make it seem complicated and mysterious, but in effect, you are simply multiplying the first three digits of your phone number (the prefix) by 10,000 so as to move it to the left four spaces to make room for the last four digits of the phone number (the suffix) to be added. For example, a prefix of 555 multiplied by 10000 equals 5550000. If you add the last four digits of your phone number (for example, 1234) then you get your original phone number (5551234.) Here’s the math formula:
Let x = the prefix and y = the suffix
Accordingly, the formula would be ((80x+1)250+2y-250)/2, so...
First, divide everything within the first set of parenthesis by 2 which gives you (80x+1)125+y-125.
Next, multiply everything in the second set of parentheses by 125 which gives you 10,000x+125+y-125.
Next, subtract the 125 from the 125 which gives you 10,000x+y.
Finally, multiply your prefix (x) by 10,000 (10,000x) and then add your suffix (y.) Voila! It’s your phone number!
Simple, yes?
A tip o’ the hat to Arnold who formulized the puzzle.