For a fraction, the sum of the numerator and the denominator is 21. If the denominator is subtracted by 4, the denominator becomes the smallest odd number. What is the original fraction?
一个分数，分子和分母的和是21，如果分母减去4，分母就变成最小的奇数，这个分数原来是多少．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">21 - 5</gadget>
<output>16</output>

<gadget id="calculator">5 / 16</gadget>
<output>5/16 = around 0.3125</output>

<result>5/16 = around 0.3125</result>