To build a road, the full length (1/5) has been built. If another 100 meters are built, the ratio of the repaired to the unrepaired is 1:3, how many meters is the total length of this road?
修一条公路，已经修了全长的(1/5)．如果再修100米，已修的与未修的比是1：3，这条公路全长多少米？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">100 / (1/20)</gadget>
<output>2_000</output>

<result>2_000</result>