In a centre code classification system, if the first digit cannot be 0, and the system uses 6-digit codes, what is the maximum number of unique centre codes possible?
Show answer & explanation
Correct answer: A
Explanation
This is a 6-digit code.
The first digit cannot be 0. ⇒ 9 options for the first position (1–9).
The remaining 5 positions can be filled with any number from 0–9. ⇒ 10 options for each.
So, the total code is:
9 × 10 × 10 × 10 × 10 × 10
= 9 × 10⁵
= 900,000