Three boxes: B1(2R),B2(1R,1B),B3(2B)B_1(2R), B_2(1R, 1B), B_3(2B)B1(2R),B2(1R,1B),B3(2B). Pick box, draw red. Prob it came from B1B_1B1?
2/32/32/3
1/21/21/2
1/31/31/3
3/43/43/4