The upper base of a trapezoid is (3/10) meters, the lower base is (2/5) meters, and the height is (5/7) meters. What is its area?
一个梯形上底(3/10)米，下底(2/5)米，高(5/7)米，它的面积是多少？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/10) + (2/5)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(1/2) * (7/10) * (5/7)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>