barrel of oil weighs 200 kilograms. After part of it is used up, there is still (3/4) of the barrel of oil left. How many kilograms are used?
一桶油重200千克，用去一部分后，还剩下这桶油的(3/4)，用去了多少千克．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">200 * (1/4)</gadget>
<output>50</output>

<result>50</result>