If that's the case, then that's interesting because it's not what I was thinking of. In my system, F would be 1101. The value of each character is independent of its context.I also think it's 1, but I may be way off. Huffman encoding against the alphabet "ABCDE" would result in A, B, C, D, and E being encoded as 10, 0111, 0101, 011, and 1, and since you told us what A through D are, E must be 1.
Also, I would be surprised if I got this right, but is the answer to your joker riddle ~0.161?