30% of a rope is used up and there are 3.5 meters left. How long is the rope in meters?
一根绳子用去30%，还剩3.5米，这根绳子长多少米．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">3.5 / (7/10)</gadget>
<output>5</output>

<result>5</result>