Time an 11-minute egg with 5 and 8-minute glasses
Asked at Jane Street, IMC
A recipe insists on boiling an egg for exactly 11 minutes. Your only timers are two hourglasses: one runs for 5 minutes, the other for 8 minutes. You may flip either glass the instant it empties, or the instant the other one empties, but you have no clock or watch.
Drop the egg in at the start and pull it out at exactly 11 minutes. How?
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.