Lelejia has a glass fish tank, which is 2.5 decimeters long and 2 decimeters wide. Lele poured 6 liters of water into the fish tank, and put some pebbles into the water. At this time, the water depth in the fish tank was measured to be 13 cm. What is the volume of these pebbles?
乐乐家有一个玻璃鱼缸，从里面量长2.5分米，宽2分米．乐乐向鱼缸中倒入6升水，又把一些鹅卵石放入水中．这时量得鱼缸中的水深是13厘米．这些鹅卵石的体积是多少？
<gadget id="calculator">13 / 10</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">2.5 * 2 * (13/10)</gadget>
<output>6.5</output>

<gadget id="calculator">6.5 - 6</gadget>
<output>0.5</output>

<result>0.5</result>