There are two oil drums, big and small. After 8.5 kg of oil is used in the large drum, it is 2.5 kg more than the small drum. It is known that the original oil in the large drum is three times that of the small drum. How much is the original oil in the small drum?
有大小两油桶，大桶油用去8.5千克后还比小桶多2.5千克，已知大桶原有油是小桶的3倍，小桶原有油多少千克？
<gadget id="calculator">8.5 + 2.5</gadget>
<output>11</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">11 / 2</gadget>
<output>11/2 = around 5.5</output>

<result>11/2 = around 5.5</result>