To build a section of road, the ratio of the repaired to the unrepaired is 1:5. After repairing another 50 meters, the ratio of repaired and unrepaired is 1:3. How many meters is this road?
修一段公路，已修和未修的比是1：5．再修50米后，已修和未修的比是1：3．这条路有多少米．
<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>6</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/4) - (1/6)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">50 / (1/12)</gadget>
<output>600</output>

<result>600</result>