Question: 2014 Winter Final - 7
Consider 4 blue balls $B_1,B_2,B_3,B_4$ and 5 red balls $R_1,R_2,R_3,R_4,R_5$. We pick 3
balls of the same color and arrange them on a horizontal line. (The order on the line matters.) How
many arrangements are there?
(a)
94
(b)
84
(c)
64
(d)
74