If 25% of a barrel of oil is used up, exactly 7 kilograms are used, so how many kilograms does the barrel of oil originally contain?
一桶油，用去25%，正好用去了7千克，则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">7 / (1/4)</gadget>
<output>28</output>

<result>28</result>