There is a pile of coal, 40% of which was burned in the first week, and 150 kg was burned in the second week, leaving 90 kg. How many kilograms did this pile of coal originally weigh?
有一堆煤，第一周烧了40%，第二周烧了150千克，还剩90千克．这堆煤原来有多少千克？
<gadget id="calculator">150 + 90</gadget>
<output>240</output>

<gadget id="calculator">40 / 100</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">240 / (3/5)</gadget>
<output>400</output>

<result>400</result>