Final answer:
To find the number of different numbers where exactly three of the digits are the same, there are 10 choices for the different digit and 9 choices for the remaining two digits, resulting in a total of 90 different numbers. The correct option is (d) 900.
Step-by-step explanation:
To find the number of different numbers where exactly three of the digits are the same, we can consider the possible arrangements of the digits. There are 10 choices for the digit that is different from the other three digits, and then there are 9 choices for the remaining two digits.
Therefore, the total number of different numbers is 10 * 9 = 90. So, the correct option is (d) 900.