Large and small two barrels of oil total 15 liters. After 1 liter of oil in the small barrel is used up, the ratio of the remaining oil to the oil in the large barrel is 2:5. How many liters of oil were originally contained in the small barrel?
大、小两桶油共15升．小桶里的油用去1升后，剩下的与大桶中油的比是2：5，小桶里原来装有多少升油？
<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">14 * (2/7)</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>