Given: The three-digit number is required

Assume we have three boxes, first box can be filled with any one of the nine digits (zero not allowed at first position) therefore possibilities are ⁹C₁, the second box can be filled with any one of the ten digits available possibilities are ¹⁰C₁, third box can be filled with any one of the ten digits available possibilities are ¹⁰C₁.

Hence number of total outcomes possible are ⁹C₁ × ¹⁰C₁ × ¹⁰C₁ = 9 × 10 × 10 = 900