cuboid fish tank measures 50cm in length, 30cm in width, and 40cm in height from the inside. The distance between the water surface and the mouth of the tank accounts for 1/8 of the height of the tank. For every liter of water, how many kilograms of water is there in the fish tank?
长方体鱼缸，从里面量长50cm，宽30cm，高40cm，水面离缸口距离占缸高的(1/8)，每升水1千克，鱼缸内有水多少千克？
<gadget id="calculator">50 / 10</gadget>
<output>5</output>

<gadget id="calculator">30 / 10</gadget>
<output>3</output>

<gadget id="calculator">40 / 10</gadget>
<output>4</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 - (1/8)</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">4 * (7/8)</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">5 * 3 * (7/2) * 1</gadget>
<output>105/2 = around 52.5</output>

<result>105/2 = around 52.5</result>