A barrel of oil, 25% is used, and there are 30 kilograms left. How many kilograms does this barrel of oil originally weigh?
一桶油，用去25%，还剩30千克．这桶油原来有多少千克．
<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">30 / (3/4)</gadget>
<output>40</output>

<result>40</result>