1) The first thing we need to do is to find the total number of visitors. This is going to be our Sample Space
31+26+2=31+28=59 Visitors altogether
2) The next thing to do is to find the favorable event. Note that we can see that 26 people purchased only one costume.
3) The final and last step is to find the probability, so we can write out the following:
Thus, this is the answer: 0.90