Calculation: (1/2)-(5/6)+(7/12)-(9/20)+(11/30)-(13/42).
计算：(1/2)-(5/6)+(7/12)-(9/20)+(11/30)-(13/42)．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<result>1/7 = around 0.142857</result>