In the renovation of an old city in a city, urban construction workers accepted the task of renovating a water pipe. They had to replace the original 6-meter-long old pipes with 9-meter-long new pipes. There are currently 270 new pipes that can be replaced. How many old pipes? (Solve with ratio)
一个城市在旧城改造中，城建工人接受了改造一条自来水管道的任务，要用每根9米长的新管道替换原来每根6米长的旧管，现有270根新管，可以换下多少根旧管？(用比例解决)
<gadget id="calculator">9 * 270</gadget>
<output>2_430</output>

<gadget id="calculator">2_430 / 6</gadget>
<output>405</output>

<result>405</result>