A rope, 30% of its total length is used up for the first time, and 40% of its total length is used up for the second time. The difference between the two times is 2 meters. What is the original length of the rope?
一根绳子，第一次用去30%，第二次又用去全长的40%，两次相差2米，这根绳子原来长多少米．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2 / (1/10)</gadget>
<output>20</output>

<result>20</result>