A person climbs a mountain, it takes 15 minutes to go up the mountain, and the speed increases (1/4) when going down the mountain, how many minutes does 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(1/4)，下山用了多少分钟．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 4</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>