A factory used an average of 9 tons of water per day in August. In September, the average daily water consumption was 8 tons. How many tons less water was used in September than in August?
一个工厂八月份平均每天用水9吨．九月份平均每天用水8吨．九月份比八月份少用水多少吨？
<gadget id="calculator">9 * 31</gadget>
<output>279</output>

<gadget id="calculator">8 * 30</gadget>
<output>240</output>

<gadget id="calculator">279 - 240</gadget>
<output>39</output>

<result>39</result>