Hi Gmat_mission,

We're told that each model of television is uniquely designated by a code made up of a particular ordered PAIR of letters and the store has 60 different models of televisions. We're asked for the minimum number of letters needed to make the 60 codes. Since the answers are numbers, we can use them 'against' the prompt and TEST THE ANSWERS.

To start, although this prompt does NOT state it, we're meant to assume that a letter CAN be used TWICE. For example, with the letters A and B, we could create 4 unique codes:
AA, AB, BA, BB

The question asks for the MINIMUM number of letters needed, so we'll start with the SMALLEST answer and work our way up...

Answer A: 6 letters --> with 6 letters, we could create (6)(6) = 36 codes. This is TOO SMALL though (we need to create 60 codes)

Answer B: 7 letters --> with 7 letters, we could create (7)(7) = 49 codes. This is TOO SMALL though (we need to create 60 codes)

Answer C: 8 letters --> with 8 letters, we could create (8)(8) = 64 codes. This covers the 60 codes we need to create, so this is the answer.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich