Tuesday, March 23, 2010

Pop quiz fallout

At the end of the two hours, Student B was still furiously scribbling away. He had accumulated a suprising amount of paper around himself. The professor came over to talk to him.
“What seems to be the problem?”
‘I don't have enough time!’
“It isn't that hard a quiz, you know. Every other student has finished. What exactly are you doing?”
‘This part, right here.’
Student B pointed to this line in the quiz:
(= (- (fib 100) (fib 99)) (fib 98))
‘I decided to evaluate this from right to left because you said that order doesn't matter. I'm still working on the (fib 98) subexpression. I think that (fib 99) and (fib 100) are going to take even longer. I can't see how anyone could get past this. I'm getting discouraged. I don't even think a computer could solve this in two hours.’

This is a key question: What, if anything, is Student B doing wrong?