A man is thinking about travelling in China by bike.His fron

A man is thinking about travelling in China by bike.His front tyre(前胎) and back tyre(后胎) can ex
A man is thinking about travelling in China by bike.His front tyre(前胎) and back tyre(后胎) can exchange(互换).If a new tyre is used for the front wheel(前轮)，it runs 3000 km at most(至多).If it is used for the back wheel(后轮)，it runs 2000km at most.If he uses two new tyres,his bike runs ___________km at most.