Li Ming went up the mountain at 2.4 kilometers per hour and reached the top of the mountain in 4.9 hours. How long does it take to go down the mountain along the original road at 2.8 kilometers per hour?
李明上山每小时行2.4千米，4.9小时到达山顶．沿原路下山每小时行2.8千米，下山用多少时间？
<gadget id="calculator">4.9 / 2.8</gadget>
<output>1.75</output>

<gadget id="calculator">2.4 * 1.75</gadget>
<output>4.2</output>

<result>4.2</result>