Uhmm.....I think probability is harder than Matrix,and some of the important things we should know are C formula and P formula
P formula : the order is important (00 and 00 : difference ==> 2 ways)
C formula : the order is not important (00 and 00 : same ==> 1 way )
That is the difference between C and P , and remember review anything we studied in class....Good luck