The iron ore yield of a certain iron ore is 45%, and 90 tons of pure iron have been smelted, how many tons of this iron ore are needed.
某种铁矿石的出铁率是45%，现已炼出纯铁90吨，则需这钟铁矿石多少吨．
<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">90 / (9/20)</gadget>
<output>200</output>

<result>200</result>