The number of four digit numbers strictly greater than 4321 that can be formed using the digits 0,1,2,3,4,5 (repetition of digits is allowed) is

Using the digits 0, 1, 2, 3, 4, 5 greater than 4321

Case I : No of 4 digit numbers starting with 5 = 1x6x6=6³

Case II : No of 4 digit numbers fixing 4, 3, 2 in first 3 places.           

              Units place can be filled with 2, 3, 4, 5 = 4

Case III :  No of 4 digit numbers begin with 43              

               Third place can be filled using 3, 4, 5 in 3 ways.

               Units place can be filled using 0 to 5 in 6 ways.

                    No. of permutations=3(6)

Case IV :

                Numbers starting with 4.

               Second place can be filled using 4, 5. Last 2 places using 0 to 5 in 6 ways

    $\therefore$ No of permutations=2(6) (6)=72

     Total=216+4+18+72=310