At first, the probability of selecting one yellow balloon was 9 out of 14.
But then one balloon was sold, so now there are only 13 to choose from.
But in addition, the balloon sold was one of the yellow ones, so now there are only 8 yellow balloons out of the (new) total of 13.
So the probability that the next balloon sold at random will be yellow is 8 out of 13, or 8/13.
