A highway has been built (2/5). If another 50 kilometers are built, (1/2) of this highway will be completed. How many kilometers is this road in total?
一条公路已修(2/5)，如果再修50千米，就正好修完这条公路的(1/2)．这条公路一共有多少千米长？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">50 / (1/10)</gadget>
<output>500</output>

<result>500</result>