After taking water-saving measures, Uncle Zhang’s family used 10 tons of water in October, which is 20% less than in September. How many tons of water did Zhang’s family save?
采取节水措施后，张大爷家10月份用水10吨，比9月份节约了20%，张家节约了多少吨水？
<gadget id="calculator">20 / 100</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">10 / (4/5)</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">(25/2) - 10</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>