A barrel of oil is 5kg, (1/2) of it was used for the first time, and (1/2)kg was used for the second time, how many kilograms are left.
一桶油是5kg，第一次用去了它的(1/2)，第二次用去了(1/2)kg，还剩多少kg．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">5 * (1/2)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">5 - (5/2) - (1/2)</gadget>
<output>2</output>

<result>2</result>