The number A is the sum of the numbers A and B (2/7), then the number B is the number A
甲数是甲、乙两数和的(2/7)，则乙数是甲数的多少
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

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

<gadget id="calculator">(5/7) / (2/7)</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>