A factory purchases a batch of coal, and transports back (1/3) of all the coal on the first day, the remaining (1/4) on the second day, and the remaining (2/5) on the third day The factory shipped back the remaining 18 tons of coal on the fourth day. How many tons of coal did the factory buy in total?
某工厂购进一批煤，第一天运回全部煤的(1/3)，第二天运回剩下的(1/4)，第三天又将余下的(2/5)运回工厂，第四天把剩下的18吨煤都运回来了，工厂共购进煤多少吨？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 / (3/5) / (3/4) / (2/3)</gadget>
<output>60</output>

<result>60</result>