For a fraction, the sum of the numerator and the denominator is 84, and after dividing it is (2/5), what is the original fraction.
一个分数，分子与分母的和是84，约分后是(2/5)，这个分数原来是多少．
<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

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

<gadget id="calculator">84 * (5/7)</gadget>
<output>60</output>

<gadget id="calculator">(2/7) / 60</gadget>
<output>1/210 = around 0.004762</output>

<gadget id="calculator">84 * (1/210)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>