25% of a barrel of oil is used up, and there is 2.5 kg left. How much does this barrel of oil weigh?
一桶油用去25%，还剩2.5千克，这桶油重多少千克？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2.5 / (3/4)</gadget>
<output>3.333333</output>

<result>3.333333</result>