If (1/3) of a rope is used up, there are 6 meters left, and (1/3) of the length of the rope at this time is used up, how many meters are left.
一根绳子，用去(1/3)后剩下6米，再用去此时绳长的(1/3)，还剩下多少米．
<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">6 * (2/3)</gadget>
<output>4</output>

<result>4</result>