A sewage treatment plant plans to purify 1,850 tons of sewage in the fourth quarter, complete 30% of the plan in October, and 35% of the plan in November. How many tons will be completed in December just to complete the plan?
一个污水处理厂计划第四季度净化污水1850吨，10月份完成计划的30%，11月份完成计划的35%，12月份再完成多少吨正好完成计划？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">1 - (3/10) - (7/20)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">1_000 * (7/20)</gadget>
<output>350</output>

<result>350</result>