The canteen of a factory used 17 tons of coal in May, which was 15% less than in April. How many tons of coal was used in April?
某厂食堂五月份用煤17吨，比四月份节约了15%，四月份用煤多少吨？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">17 / (17/20)</gadget>
<output>20</output>

<result>20</result>