Question

The total number of three-digit numbers, with one digit repeated exactly two times, is ______.

Answer 1

The correct answer is: 243

C-1 : All digits are non-zero

$C_2^9.2.\frac{3!}{2}=216$

C-2 : One digit is 0

0,0,x⇒9C1.1.=9

0,x,x⇒9C1.2.=18

Total = 216 + 27 = 243