To build a road, 50% of the total length was repaired in the first week, and 30% of the total length was repaired in the second week, and 800 meters were repaired in the first week than in the second week. How many meters of this road are left to be repaired?
修一条公路，第一周修了全长的50%，第二周修了全长的30%，第一周比第二周多修800米，这段公路还剩多少米没修？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(1/2) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">800 / (1/5)</gadget>
<output>4_000</output>

<gadget id="calculator">1 - (1/2) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4_000 * (1/5)</gadget>
<output>800</output>

<result>800</result>