RenB
Of the four-digit positive integers that are greater than 4000, how many have three digits that are equal to each other and one digit that is not equal to the other three?
A. 162
B. 215
C. 216
D. 240
E. 324
Case 1: The thousands digit repeats thrice
X _ _ _
The thousand's place can be selected in 6 ways ( one among 4, 5, 6, 7, 8, and 9).
As the digit in the thousand's place repeats thrice, we need another digit. This digit can be selected in 9 ways (all digits from 0 to 9 except the one selected in the thousand's place).
The last three positions of the number can be interchanged to form various arrangments, hence the total number of digits that can be formed with the thousand's digit repeating thrice =
\(6 * 9 * \frac{3!}{2!} = 162\)
Case 2: Thousands digit is not the repeating digit
X Y Y Y
The thousand's place can be selected in 6 ways ( one among 4, 5, 6, 7, 8, and 9).
The second digit can be selected in 9 ways (all digits from 0 to 9 except the one selected in the thousand's place).
The last three positions of the number can be interchanged to form various combinations, hence the total number of digits that can be formed with the thousand's digit repeating thrice =
\(6 * 9 * \frac{3!}{3!} = 54\)
This case also has the possibility of the number being 4000. However, as we need the integers that are above 4000, we need to subtract 1 from the obtained result.
The total number of digits that can be formed with the thousand's digit repeating thrice =
\(54 - 1 = 53\)
Total : 53 + 162 = 215
Option BSimilar Question to Practice :
https://gmatclub.com/forum/of-the-three ... 35188.html