The sum of the numerator and denominator of a fraction is 21. If 19 is added to the denominator, the new fraction will be (1/4) after division. What is the original fraction?
一个分数的分子和分母之和是21，如果分母加上19，新的分数约分后是(1/4)，原分数是多少．
<gadget id="calculator">21 + 19</gadget>
<output>40</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 * (1/5)</gadget>
<output>8</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 * (4/5)</gadget>
<output>32</output>

<gadget id="calculator">32 - 19</gadget>
<output>13</output>

<gadget id="calculator">8 / 13</gadget>
<output>8/13 = around 0.615385</output>

<result>8/13 = around 0.615385</result>