There are ten students. Eight of them have travelled to Europe, seven of them speak Spanish and six of them study math. How many students have travelled to Europe, speak spanish and study math?
Well, I know that I have to find the intersection between the three sets (Europe, Spanish and Math) but as I haven't been given any other intersection (like "two of the students that speak Spanish also have travelled" or something like that) I feel that I need more info...
As already written in the comments, you are right; the question cannot be answered based only on the information provided.