Markr asked: How high is the jumper's center of mass?
You're on the right track but no more clues..
Come on you maths eggheads, it's a simple enough question-
If a high-jumper can jump 7 feet on earth, how high would he be able to jump on the moon where the gravity is one-sixth less?
You needn't be exact, just an "about" figure will do.
When all your guesses are in (or if nobody can make a guess within the next few days) I'll scan and post the paragraph from Clarke's book that gives the answer..