Answer:
 2/7
Step-by-step explanation:
The total of all probabilities of possible outcomes must be 1, so we require ...
 5x +2x +3x +4x = 1
 14x = 1 . . . . . . . . collect terms
 x = 1/14 . . . . . . . divide by 14
Then the probability of selecting a yellow marble is ...
 4x = 4(1/14) = 2/7