Question

A spider must eat 3 flies a day to survive. After he has taken his three he quits for the day. For any fly that crosses his path, he has a 50% chance of nabbing that fly. Given that five flies have sailed past the spider today (some surviving and some not), find the chance of survival of next fly.

Answer 1

The answer is 0.75.
(1/2)*1 + (1/2)*0.5 = 0.75