The standard serial numbers for a bill are 2 letters followed by 5 digits. How many bills are possible if letters and digits can be repeated?  Answers.
A) 26 × 26 × 100 000  B) 24³ × 10 ×10 000  C) 26³ × 10 000  D) 26 × 25 × 24 × 10  E) 26 x 26 x 10 000
OFFICIAL SOLUTION:   (A) The formula for permutations of events is the product of the number of ways each event can occur. There are 26 letters and 10 digits. So there are 26 × 26 options for the two letters, and 10 × 10 × 10 × 10 x 10 for the five digits. The number of bills is 26 × 26 × 10 × 10 × 10 × 10 x 10 = 26 x 26 x 100 000.   The correct answer is choice (26 × 26 × 100 000).
<result>A</result>
The standard serial numbers for a bill are 2 letters followed by 5 digits. How many bills are possible if letters and digits can be repeated?