Make the smallest 4-digit number using the digits 7, 4, 9 and 0 without any repetition.

The given digits are 7, 4, 9 and 0.

To obtain the smallest number, arrange the digits in ascending order, 0 < 4 < 7 < 9

0479 is not a four-digit number, this is a 3-digit number. 

So we place 0 at the hundreds place to make it a four-digit number.

Thousands       Hundreds          Tens           Ones    

         4                     0                     7                9 

Therefore, the required number is 4079.