He has to either win all the games or he can loose one and win the rest out of four
Probability of winning all four =(23)4=1681
loose firsrt and win all three =13.13.23.23=481
Loose second and win rest =23.13.13.23=481
Loose third and win rest =23.23.13.13=481
Loose fourth and win rest =23.23.23.13=881
⇒ probability of winning atlest three =1681+481+481+481+881=3681=49