Question

There is a bag filled with 4 blue and 5 red marbles.

Answer 1

1) first pick red 5/9 blue 4/9

2) second pick when red has been picked red now becomes 4/8, blue stays 4/8

2) Second pick when blue has been picked blue now becomes 3/8, red stays 5/8

Mind you, you only need both different colours so:

first pick red 5/9 x sec pick blue 4/8 = 20/72

and first pick blue 4/9 x sec pick red 5/8 = 20/72

add both up 20/72 + 20/72 = 40/72 = 5/9