Question 1111274
 There are 4 independent events and each event can occur in 10 possible ways. Since the events are independent, you multiply them to find the total number of possible combinations. 

You can pick the first digit 10 different ways, the 2nd digit 10 different ways, the third digit 10 different ways, and the 4th digit 10 different ways.
So there are 10*10*10*10=10000 possible ways to pick the digits (Answer).