the engineer, the undergrad, and primary school maths
Vehicle 1 takes 7 hours to get from A to B; vehicle 2 takes 8 hours to get from B to A. If both starts moving at the same time towards each other, how long does it take before they pass each other?
The undergrad tried to smoke out an answer by applying his newly-learned kinematics equations, ended up with 0 = 0. He couldn't be bothered and went back to sleep.
The undergrad rolled a few times on his bed, then sprung up, went to his engineer brother, grab a pen and paper, wrote 2 simple lines of equation, solved.
Then he went back to sleep.
(while his brother was whining how to explain to the kid)
Lesson of the day: if you can't solve a problem, go and sleep.