There is a colored ribbon, after one-third of it is used up, there is still 20 meters left, how many meters is this colored ribbon in total?
有一根彩带，用去它的三分之一后，还剩下20米，这根彩带一共有多少米．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">20 / (2/3)</gadget>
<output>30</output>

<result>30</result>