For a pile of coal, (1/5) tons are used for the first time, and (2/5) tons are used for the second time, exactly 1 ton is used for the two times. How many tons does this pile of coal have?
一堆煤，第一次用去(1/5)，第二次用去(2/5)吨，两次正好用去1吨，这堆煤原有多少吨？
<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 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(3/5) / (1/5)</gadget>
<output>3</output>

<result>3</result>