Two tourist A and B who are at a distance of 40 km from their camp must reach it together in the shortest possible time. They have one bicycle and they decide to use it in turn. ‘A’ started walking at a speed of `5 km hr^(1)` and B moved on the bicycle at a speed of `15 km hr^(1)`. After moving certain distance B left the bicycle and walked the remaining distance. A, on reaching near the bicycle, picks it up and covers the remaining distance riding it. Both reached the camp together. (a) Find the average speed of each tourist. (b) How long was the bicycle left unused?
