How many four-digit numbers are there such that all four digits are different and the first digit is not zero? Choose the correct choice:
A) 1504 B) 2648 C) 3720 D) 5832 E) 8105
All four digits are different and first digit is not zero.   So first digit can be filled in 9 ways.   And, second digit can be filled in 9 ways.   And, third digit can be filled in 9 ways.   And, fourth digit can be filled in 8 ways.   Total ways = 9*9*9*8= 
<gadget id="calculator">9*9*9*8</gadget>
<output>5_832</output>
5832   Hence option (5832).
<result>D</result>
How many four-digit numbers are there such that all four digits are different and the first digit is not zero?