Calculation: (5/7)-(2/21)-(3/21).
计算：(5/7)-(2/21)-(3/21)．
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">2 / 21</gadget>
<output>2/21 = around 0.095238</output>

<gadget id="calculator">3 / 21</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(5/7) - (2/21) - (1/7)</gadget>
<output>10/21 = around 0.47619</output>

<result>10/21 = around 0.47619</result>