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A three-digit code must be used to access a computer file. The first digit must be an A or a B. The second digit must be a number between 0 and 9. The final digit is a single letter from the alphabet from A to Z. How many possible access codes can there be?

A 520

There are 2 possibilities for the first digit (A or B), 10 possibilities for the second digit (0 to 9) and 26 possibilities for the third digit. Using the multiplication principle, 2 × 10 × 26 = 520.