It took 15 minutes to go up the mountain alone, and the speed increased by 25% when going down the mountain. How long did it take to go down the mountain?
一个人登山，上山用了15分钟，下山时速度加快了25%，下山用了多长时间？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(1/15) * (5/4)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>