A man is thinking about travelling in China by bike.His front tyre(前胎) and back tyre(后胎) can exA 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.
问题描述：
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.
答
2400
答
x+(2000-x)*3/2=(3000-x)*2/3+x(要走最远2轮要同时耗尽,x代表*1作为后轮时行驶的路程)
解得：x=1200
sum=1200+（2000-1200）*3/2=2400
2400