Three cars, slow, medium and fast, start from the same place at the same time and chase a cyclist in front along the same road. The speeds of these three cars are 10 km/h, 15 km/h, and 30 km/h respectively. It is known that the slow car and the medium car took 4 hours and 2 hours to catch up with the cyclist respectively. Then the fast car took How many hours to catch up with the cyclist.
慢、中、快三辆车同时从同地出发，沿同一公路追赶前面一个骑车人．这三辆车的速度分别是10千米/小时、15千米/小时、30千米/小时，已知慢车、中车分别用了4小时、2小时追上骑车人，那么快车用了多少小时追上骑车人．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>