A pile of coal uses up (2/5) of the total amount. At this time, the amount used is 30 tons less than the rest. How many tons does this pile of coal have?
一堆煤，用去总数的(2/5)，这时用去的比剩下的少30吨，这堆煤共有多少吨？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">30 / (1/5)</gadget>
<output>150</output>

<result>150</result>