In which order should the four different digits be arranged to obtain the largest 4 digit number

Given: The digits 0, 1, 2, 3,....9

To find: The largest four-digit number

Solution:

The digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Among the above, the largest four digits are: 6, 7, 8, 9

To get the largest 4 digit number with four different digits, we have to arrange them in descending order as follow

9 8 7 6

So, 9876 is the largest 4-digit number obtained by arranging four different digits.