how many four-digit numbers can be formed that haVe the digit 5 used exactly once in them? given ans is 3033 which i am not getting

Hi,

There are 4 cases possible-

There are 4 cases possible-

5 _ _ _ -> Here the other 3 digits can selected in 9 ways each (5 is used only once) => 9 X 9 X 9 = 729 

_ 5 _ _ -> Here the thousandth digit can be selected in 8 ways (no 5 no 0) and others in 9 ways => 8 X 9 X 9 = 648

Same goes for the cases below.

_ _ 5 _

_ _ _ 5

So, total will be 729 + 648X3 = 2673

So, 2673 must be the answer.