By definition of conditional probability,
P(B | A) = P(A ∩ B)/P(A) = (13/25) / (13/20) = 20/25 = 4/5
Ratio is 10:16, so to win 50, its 50:190, so you need to play 190 games to win 50
60 = 40% * x ;
60 = ( 40 / 100 ) * x ;
60 = 2x / 5 ;
2x = 300 ;
x = 300 / 2 ;
x = 150 is full marks.