From home to the library, Xiaohua can walk for 2.5 hours at a speed of 4 kilometers per hour. How many hours does it take for him to walk home along the same road at a speed of 5 kilometers per hour?
小华从家到图书馆，按每小时4千米的速度，步行2.5小时可以到达．他沿着原路回家，按每小时5千米的速度，需要步行多少小时？
<gadget id="calculator">2.5 / 5</gadget>
<output>0.5</output>

<gadget id="calculator">4 * 0.5</gadget>
<output>2</output>

<result>2</result>