barrel of oil weighs 4 kilograms, 25% of the oil is used for the first time, and (1/4) kilogram is used for the second time, how much is left?
一桶油重4千克，第一次用去了25%，第二次用去了(1/4)千克，还剩下多少．
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">4 - 1 - (1/4)</gadget>
<output>11/4 = around 2.75</output>

<gadget id="calculator">(11/4) / 4</gadget>
<output>11/16 = around 0.6875</output>

<result>11/16 = around 0.6875</result>