Pile a pile of logs into a trapezoid, with 3 logs on the top layer and 7 logs on the bottom layer, making a total of 5 layers, and the lower layer has 1 more log than the upper layer. How many logs are there in total?
把一堆圆木堆成梯形，最上面一层有3根，最下面一层有7根，一共堆了5层，下层都比上一层多1根．这堆圆木一共有多少根．
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">10 * (5/2)</gadget>
<output>25</output>

<result>25</result>