There was a pile of coal in the cafeteria. After (1/5) was used up, another 4.5 tons were brought in, which was 25% more than the original pile. How many tons did the pile of coal weigh?
食堂原有一堆煤，用去(1/5)后，又运来4.5吨，这时比原来增加了25%，原来这堆煤重多少吨？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<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">(5/4) - (4/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">4.5 / (9/20)</gadget>
<output>10</output>

<result>10</result>