Answer:
6 combinations with a sample space of {DMC,DCM,CMD,CDM,MCD,MDC}
Explanation:
Here, we are looking for the possible combinations of books since the order doesn't matter:
Method 1: You can take the factorial of 3 since order doesn't matter, which will mean 3!=3*2*1=6 combinations
Method 2: List all the possible combinations for your sample space
DMC
DCM
CMD
CDM
MCD
MDC
Either method you choose, you'll end up with the same result of 6 combinations with a sample space of {DMC,DCM,CMD,CDM,MCD,MDC}