A factory used 510 tons of water last month, 260 tons in the first half of this month, and 210 tons in the second half of the month. How much less water is used this month than last month?
某工厂上个月用水510吨，这个月上半月用水260吨，下半月用水210吨，这个月用水量比上个月少多少？
<gadget id="calculator">260 + 210</gadget>
<output>470</output>

<gadget id="calculator">510 - 470</gadget>
<output>40</output>

<result>40</result>