A batch of cement was shipped to the construction site, 40% of the total amount was used on the first day, and 9 tons were used less on the second day than on the first day, leaving 17.5 tons. How many tons is this batch of cement originally?
建筑工地运来一批水泥，第一天用去总数的40%，第二天比第一天少用9吨，此时还剩17.5吨．这批水泥原有多少吨？
<gadget id="calculator">17.5 - 9</gadget>
<output>8.5</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 2</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">8.5 / (1/5)</gadget>
<output>42.5</output>

<result>42.5</result>