What is the largest five digit number which can be formed using the digits 7, 8, 5, 4 and 9, if only one digit can be repeated twice?
99875
Since we are required to form the largest 5 digit number, the leftmost digit at ten-thousand's place will be the largest out of the 5 given digits, that is, 9.
Since one digit can be repeated, we can choose the repeating digit to be either of 9,8,7,5 or 4.
Since we want the largest possible number, we choose to repeat the digit 9.
Thus, digit at thousand's place = 9
Similarly, we can say,
Digit at hundred's place = largest digit after 9 =8
Digit at tens' place = largest digit after 9 and 8 = 7
Digit at ones' place = largest digit after 9, 8 and 7 = 5
Placing the digits at their respective places we get 99875