A construction site has a batch of rotors, 35% of the total is used on the first day, 25% of the total is used on the second day, and 2.5 tons less are used on the second day than on the first day. How many tons are there in this batch of rotors?
一个工地有一批转头，第一天用去总数的35%，第二天用去总数的25%，第二天比第一天少用去2.5吨，这批转头一共有多少吨？
<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(7/20) - (1/4)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2.5 / (1/10)</gadget>
<output>25</output>

<result>25</result>