Question 315397
There are two positions to fill. 

In the first spot, there are five possibilities: A, B, C, D, or E. 

In the second spot there are four remaining possibilities (because one has already been selected for the first spot). 

If A is the first one, the second one could be one of the remaining four: 
AB
AC
AD
AE

If B is the first one, the second one could be one of the remaining four: 
BA
BC
BD
BE


If C is the first one, the second one could be one of the remaining four: 
CA
CB
CD
CE


If D is the first one, the second one could be one of the remaining four: 
DA
DB
DC
DE


If E is the first one, the second one could be one of the remaining four: 
EA
EB
EC
ED

Hence there are 20 possibilities. 

Actually, you don't even have to list them all out like this. Just recognize the pattern that there are 5 possibilities for the first one, and for each of them there are 4 for the second one (after the first has already been selected). Thus we multiply, 4 * 5 to get 20.