The task of building a simple prefabricated house in a certain disaster-stricken area in Sichuan was divided between the army and the victims on a 1:2 basis. The army built 20 rooms a day, and the victims built 25 rooms a day. How many board houses to build?
四川地震某灾区搭建简易板房任务，按1：2分给部队和灾民去完成，部队每天搭建20间，灾民每天搭建25间，两组人马同时开工，最后部队比灾民提前30天完成，部队搭建多少间板房？
<gadget id="calculator">25 * 30</gadget>
<output>750</output>

<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 - 25</gadget>
<output>15</output>

<gadget id="calculator">750 / 15</gadget>
<output>50</output>

<gadget id="calculator">50 * 20</gadget>
<output>1_000</output>

<result>1_000</result>