having a hard time getting an grasp on percentages when used in the following type of question.

What percentage of the total cash was held by George.

         # of $100 bills      # of $50 bills   # of $20 bills

mike        137                      115                  31

george       132                     319                 30

Jake          43                       116                 79 

if anyone can help or point me in the right direction on this website that would be greatly appreciated. Thank you