the probability of the outcome of the color/ Divided by the total of how many colors there are.
in this case there is one yellow, but it may very well be smaller than the other colors so it does not have the probability of 1/4, unless they tell you that all the color sizes are equal.
so now, instead,we shall base it off of the Trial Numbers. Which would be 10/50, which can be reduced to 1/5. :)
Good Luck!
(But please ask your teacher or mentor if this is correct.)