Write the smallest 4-digit number formed using the digits 8,3,0,1.

The ascending order of the given numbers 8,3,0,1 is:

0<1<3<8 

A number cannot begin with 0, so we will put it in the second place. 

The smallest digit (other than 0) is 1. 

Therefore, the number will begin with 1.

Thus, the smallest number formed is 1038.

Hence, the smallest 4 digit number formed is 1038.