A factory used 540 tons of water in May, 10% less than last month. How many tons did it use last month?
某工厂五月份用水540吨，比上个月少用10%，问上个月用水多少吨？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">540 / (9/10)</gadget>
<output>600</output>

<result>600</result>