people repair 840 meters of road in 10 days. At this speed, 20 people will repair 4200 meters. How many days will it take to complete the road. (Solve with ratio)
5个人10天修公路840米，照这样的速度，20人要修4200米，需要多少天修完全程．(用比例解)
<gadget id="calculator">4_200 * 5 * 10</gadget>
<output>210_000</output>

<gadget id="calculator">20 * 840</gadget>
<output>16_800</output>

<gadget id="calculator">210_000 / 16_800</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>