This is actually easy, because you just have to add up the 25 +15 and that would get you 40. Then you would have to add 20 to the 40 and that would be 60, so that would make 40/60 chance that she wouldn't get blue.
And if you need it in a percentage, then you can just convert this into a percentage which would be, 66.666666666667%, also known as 66.67%