A water pipe uses 20% of its total length for the first time, and 30 meters less than the first time for the second time, leaving 150 meters left. How many meters is this pipe?
一根自来水管第一次用去全长的20%，第二次比第一次少用去30米，这时还剩150米．原来这根水管长多少米？
<gadget id="calculator">150 - 30</gadget>
<output>120</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5) - (1/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">120 / (3/5)</gadget>
<output>200</output>

<result>200</result>