Question 299498
      (a) The leading digit cannot be zero
          The first digit is 1 of 8 the next 2 are 1 of 10.
          9*10*10=900 ans.

      (b) the leading digit cannot be zero and no repetition of digits
          9*9*8=648 ans.

      (c) the leading digit cannot be zero and the number must be a multiple of 5 
          9*8*1=72 ans.
      (d) the number is at least 400
          1*9*8=72 ans.