68. In the USSR Cup football games, after the qualifying matches, the football teams are divided by lot into two equal groups. In each group, the winner of that group is determined separately, and the two winners meet in the cup final. Let the total number of teams that have passed the qualifying matches be 20.

a) What is the probability that the two strongest teams will end up in different groups?

b) What is the probability that the four strongest teams will end up in the same group? What is the probability that the four strongest teams will end up in the same group for two consecutive years?

c) What is the probability that the four strongest teams will be split into two different groups, with two in each group?
68. a) $\frac{10}{19}$.

b) $\frac{C_{16}^{6}}{\frac{1}{2} C_{20}^{10}}=\frac{28}{323} \approx 0.08 ; \quad\left(\frac{28}{323}\right)^{2} \approx 0.0064$.

c) $\frac{3 C_{16}^{8}}{\frac{1}{2} C_{20}^{10}}=\frac{135}{323} \approx 0.42$.