For a fraction with a denominator greater than 10 and less than 30, if adding twice the denominator to both the numerator and the denominator of the fraction, the resulting fraction is exactly 9 times the original fraction, what is the original fraction?
一个分母大于10且小于30的分数，若在这个分数的分子与分母上都加上分母的2倍后，所得分数恰好是原分数的9倍，则原分数是多少．
<gadget id="calculator">1 / 13</gadget>
<output>1/13 = around 0.076923</output>

<result>1/13 = around 0.076923</result>