解:把路程看成1,得到時(shí)間系數(shù)
去時(shí)時(shí)間系數(shù):1/3÷12+2/3÷30
返回時(shí)間系數(shù):3/5÷12+2/5÷30
兩者之差:(3/5÷12+2/5÷30)-(1/3÷12+2/3÷30)=1/75相當(dāng)于1/2小時(shí)
去時(shí)時(shí)間:1/2×(1/3÷12)÷1/75和1/2×(2/3÷30)1/75
路程:12×〔1/2×(1/3÷12)÷1/75〕+30×〔1/2×(2/3÷30)1/75〕=37.5(千米)