How many three-digit odd numbers are there?

Available digits for filling any place = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}

Since the thousand's place cannot be zero, the number of ways of filling the thousand's place is 9.

Number of ways of filling the ten's place = 10

Number of ways of filling the unit's place = 5  {1, 3, 5, 7, 9}

Total 3-digit odd numbers $=9 \times 10 \times 5=450$