There is a rope, 20% of its total length is cut off for the first time, and 3 meters are cut off for the second time, so half is left. How many meters is this rope?
有一条绳子，第一次剪去全长的20%，第二次剪去3米，这时正好剩下一半，这条绳子原来是多少米？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/5) - (1/2)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3 / (3/10)</gadget>
<output>10</output>

<result>10</result>