The telephone company wants to add an area code composed of 2 letters to every phone number. In order to do so, the company chose a special sign language containing 524 different signs. If the company used 522 of the signs fully and two remained unused, how many additional area codes can be created if the company uses all 524 signs? Choose the correct choice from the following choices
A) 46	B) 248	C) 2092	D) 15,128	E) 30,256

Rationale: # of 2 - letter codes possible from 524 different signs = 524 * 524 . # of 2 - letter codes possible from 522 different signs = 522 * 522 . the difference = 524 ^ 2 - 522 ^ 2 = ( 524 - 522 ) ( 524 + 522 ) = 2092 . answer : c .
Answer: C