Two candles of the same length can be burned out in 5 hours for each one, and only 3 hours for the second one. If the two candles burn at the same time, after how many hours, the remaining length of the first one is the remaining length of the second one. 3 times the length.
两根同样长的蜡烛，每一根5小时可烧完，第二根烧完只需3小时，两根蜡烛同时燃烧，经过多少小时后，第一根剩下的长度是第二根剩下长度的3倍．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">3 * (1/3)</gadget>
<output>1</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 / (4/5)</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>