A registration code has two letters (from the letters, repetition allowed) followed by three digits (repetition allowed). How many codes are possible?
Answer and explanation
Correct answer: C.
- Step 1: Multiplication principle: . Step 2. . **Answer: . Why not the others:** : This forbids repeated letters and digits: . : This allows repeated letters but forbids repeated digits. : This forbids repeated letters but allows repeated digits: .
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