Question

Four persons can cross a bridge in 3,7,13,17 minutes. Only two can cross at a time. Find the minimum time taken by the four to cross the bridge.

Answer 1

Answer:

At minute 0, persons C (13) and D (17) begin crossing. At minute 13, person C is finished and person B (7) starts. At minute 17, D is finished and A (3) can start. At minute 20, both A and B finish.