Calculation: (2/5)+(4/7)-(2/5)+(1/7).
计算：(2/5)+(4/7)-(2/5)+(1/7)．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) - (2/5)</gadget>
<output>6/35 = around 0.171429</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(2/5) + (6/35) + (1/7)</gadget>
<output>5/7 = around 0.714286</output>

<result>5/7 = around 0.714286</result>