The school used 100 tons of water in October, saving (1/5) compared to September. How many tons of water was used in September?
学校十月份用水100吨，比九月份节约了(1/5)，九月份用水多少吨？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">100 / (4/5)</gadget>
<output>125</output>

<result>125</result>