The two piles of coal are 81 tons in total, the first pile is used (2/3), and the second pile is used 60%. Combining the two piles of coal is the original first pile (5/6). How many tons was the first pile of coal?
两堆煤共81吨，第一堆用去(2/3)，第二堆用去60%，把两堆煤合起来是原来第一堆的(5/6)．原来第一堆煤有多少吨．
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">81 * (3/5)</gadget>
<output>243/5 = around 48.6</output>

<gadget id="calculator">81 - (243/5)</gadget>
<output>162/5 = around 32.4</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(5/6) - 1 - (3/5)</gadget>
<output>-23/30 = around -0.766667</output>

<gadget id="calculator">(2/3) + 1 + (-23/30)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(162/5) / (9/10)</gadget>
<output>36</output>

<result>36</result>