There are 20 water pipes in the bottom layer of a pile of water pipes, and 8 pipes in the top layer.
一堆水管最下层有20根，最上层有8根，上比下每层少1根，这堆水管一共有多少根．
<gadget id="calculator">8 + 20</gadget>
<output>28</output>

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">12 + 1</gadget>
<output>13</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<gadget id="calculator">28 * (13/2)</gadget>
<output>182</output>

<result>182</result>