The sum of the upper and lower bases of a trapezoid is 40 decimeters, and the height is 5 decimeters. What is the area in square decimeters?
一个梯形上底与下底的和是40分米，高是5分米，面积是多少平方分米．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">40 * (5/2)</gadget>
<output>100</output>

<result>100</result>