Pass the Parcel
Five friends A, B, C, D, E stand in a circle. A holds a ball. Every second, whoever holds the ball throws it to one of the other four friends, chosen uniformly at random. What is the expected number of throws until E first receives the ball? Give an exact number.
Related problems & prerequisites
Worth solving first
- First Heads Wins 3.0/10
- Seven Before Eight 2.0/10
Source: Classic exercise in wide circulation; no traceable original source. Statement written for AxiomIQ.