Every passenger is either in the first class or in the tourist class of a cruise. Each passenger is in tourist class if and only if he is wealthy. Some passengers are wealthy. Not all passengers are wealthy.

From the above statement, which of the following conclusions can be certainly drawn.

Let $$a$$ denote the number of passengers who are in first class, and $$b$$ denote the number of passengers who are in the tourist class. The total number of passengers is $$a+b$$. We are given that some passengers are wealthy, but not all. It can be inferred that the remaining passengers are not wealthy. All of the non- wealthy passengers will definitely be in the first class, and all the wealthy passengers will definitely be in the tourist class. Thus $$b> 0$$ and $$b<a+b$$ gives $$a>0$$, hence some of the passengers will be non- wealthy and they'll sit in the first class. Some of the passengers, therefore, are in tourist class.