A person walks a distance at the same speed. If he walks 0.5 kilometers more per hour than before, he only needs (4/5) of the original time to walk this distance. If he walks 0.5 kilometers less per hour than before, then he walks this distance more than before It takes 2.5 hours, what is the length of this distance in kilometers?
一个人以相同的速度走一段路．假如他每小时比原来多走0.5千米，他走这段路只需要原来时间的(4/5)，假如他每小时比原来少走0.5千米，那么他走这段路就比原来多花2.5小时，求这段路程长是多少千米？
<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(5/4) - 1</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">0.5 / (1/4)</gadget>
<output>2</output>

<gadget id="calculator">2 - 0.5</gadget>
<output>1.5</output>

<gadget id="calculator">2.5 / 0.5</gadget>
<output>5</output>

<gadget id="calculator">1.5 * 5</gadget>
<output>7.5</output>

<gadget id="calculator">2 * 7.5</gadget>
<output>15</output>

<result>15</result>