Student Exam Excuses

Two engineering students had thoroughly impressed their Professor in one of their core subjects, having achieved the highest marks throughout the semester's continuous assessments. Being one to give credit where due, the Prof made no secret of his two prize students, continually praising their achievements.

The weekend before their final exam (which was to contribute fifty percent of their final grade,) these two geniuses felt they deserved a hard earned break and so went out of town to celebrate their 'pending' success.

Having partied late all weekend (and then some,) the two students overslept Monday morning, missing their final exam! Never lacking in will power, they were determined not to fail, having come so far, so well. Upon rolling into town, they appealed to the Prof, and conveniently explained that they had a flat tire while out visiting and that it was not their fault for missing the exam.

The Professor was very understanding and rescheduled their exam to the next day, much to the student's delight! They arrived at his office the next morning, where he sat them on each side of his desk facing opposite walls, while he worked on grading the other exams. They opened their examination books and were both pleased with the first easy 10-point question that came directly from a homework assignment. You could hear nothing but the quick writing of their pencils in the room, until they both flipped the page, almost at the same time, where the second question read thusly...

"90 points: Which tire?"