The probabilities of A and B solving the problem are  respectively.
     the probabilities of A and B not solving the problems are  i.e.,  respectively.
      probabilities that problem is not solved by A and BÂ
     probability that the problem will be solved =Â
      Â
The probabilities of three students solving the problem are   respectively.
   proabilites of three students not solving the problem are
          Â
      the probability that the problem is not solved by any one of them
                 Â
      probability that the problem will be solved by atleast one of them
                  Â
Let W , L and T denote the events that the team wins, loses and ties respectively.
∴ P (W) = 0.7, P (L) = 0.2, P (T) = 0.1
Required probability = P (team wins at least two games but not loses)
= P (WWT) + P (WTW) + P (TWW) + P (WWW)
= P (W) P (W) P (T) + P (W) P (T) P (W) + P (T) P (W) P (W) + P(W) P(W) P(W)
= 3 [P (W) P (W) P (T)] + P (W) P (W) P (W)
= 3 [(0.7) (0.7) (0.1) + (0.7) (0.7) (0.7)
= 3 × 0.049 + 0.343 = 0.147 + 0.343
= 0.49