The sum of the numerator and denominator of a fraction before division is 36, and after division is (4/5), find the original fraction.
一个分数约分前分子、分母的和是36，约分后是(4/5)，求原来的分数．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">36 * (4/9)</gadget>
<output>16</output>

<gadget id="calculator">36 - 16</gadget>
<output>20</output>

<gadget id="calculator">(4/9) / 20</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">36 * (1/45)</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>