Question 21
Three brothers Kai, Kay and Ken travel from their house to their grandparents’ house. The distance they need to travel is 30 km long. Three brothers have only one motorbike and one skateboard. The motorbike has a maximum speed of 60 km/h and it can carry a maximum of 2 people at a time. The skateboard has a maximum speed of 15 km/h and only one person can ride it. Three brothers leave home at the same time and they need at least “x” minutes to reach grandparents’ house. Find the value of “x”.
Explicit grading convention for the source’s intended one-shuttle interpretation: the motorbike first takes two brothers to the destination; one stays there, and the driver returns once to collect the skateboard rider, then both ride to the destination. There is no walking, and transfer is instantaneous. The original wording does not specify these transfer and walking rules; the solution’s verified minimum is confined to this stated model.
Explicit grading convention for the source’s intended one-shuttle interpretation: the motorbike first takes two brothers to the destination; one stays there, and the driver returns once to collect the skateboard rider, then both ride to the destination. There is no walking, and transfer is instantaneous. The original wording does not specify these transfer and walking rules; the solution’s verified minimum is confined to this stated model.