Probability

There is a probability problem that i have thought about quite often in the past when im on my way to school... Say you come to school around 7:30 everyday. Judging by my experience most of the parking lots are fairly empty at this time. Not knowing the actual numbers, lets assume there are 150 parking spots in sophomore lot. At around 7:30 there are about 15 cars in the lot, taking up the nicest and closest parking spots. This leaves about 135 spots left. There is one spot in particular that i like and it is towards the front and next to a trash can. Usually this spot is open. My problem today, is what is the probability that the spot that i like will be taken by the time i got to school at 7:30? 

Since the first 15 cars pick from the top parking spots, we will say that there are 25 top parking spots that they choose from, from day to day. The spot next to the trash can is included in this number. So, I can looking for this spot to be open, so in order for that to happen, the 15 drivers must pick one of the other 24 spots. The probability of them picking the spot next to the trash can, not including their intellect, is (1/25)*15=.6=60%

Now, having the probability that my spot would be taken, we can find out the probability that It will be open very easily. 100%-60%=40%