(2/5) of a barrel of oil is used up, leaving (2/5) tons. How many tons is this barrel of oil originally?
一桶油用去(2/5)，还剩(2/5)吨．这桶油原来有多少吨？
<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">(2/5) / (3/5)</gadget>
<output>2/3 = around 0.666667</output>

<result>2/3 = around 0.666667</result>