Uncle went to climb the mountain, he went up the mountain at 2.2 kilometers per hour, and reached the top of the mountain in 2.5 hours. How many hours does it take to go down the mountain at 4 kilometers per hour?
叔叔去爬山，上山每小时行2.2千米，2.5小时到达山顶．下山时每小时走4千米，下山要用多少小时？
<gadget id="calculator">2.5 / 4</gadget>
<output>0.625</output>

<gadget id="calculator">2.2 * 0.625</gadget>
<output>1.375</output>

<result>1.375</result>