In a pile of coal, the total (3/10) has been burned and 50 tons more, and the remaining coal is 350 tons less than the total (3/4). How many tons does this pile of coal have? (Solution of column equation)
一堆煤，已烧了总数的(3/10)还多50吨，剩下的煤比总数的(3/4)少350吨．问这堆煤原有多少吨？(列方程解)
<gadget id="calculator">350 - 50</gadget>
<output>300</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(3/4) - 1</gadget>
<output>-1/4 = around -0.25</output>

<gadget id="calculator">(3/10) + (-1/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">300 / (1/20)</gadget>
<output>6_000</output>

<result>6_000</result>