A piece of steel, 3 meters are used up, the ratio of the used to the remaining is 1:4, how many meters is left in this piece of steel.
一根钢材，用去3米，用去的与剩下的比是1：4，这根钢材还剩多少米．
<gadget id="calculator">1 + 4</gadget>
<output>5</output>

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

<gadget id="calculator">3 / (1/5)</gadget>
<output>15</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>