The sum of the numerator and the denominator of a fraction is 90. After dividing the fraction, it is (2/13). What is the original fraction?
一个分数分子与分母的和是90，将分数约分后是(2/13)，原来这个分数是多少．
<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">13 / 15</gadget>
<output>13/15 = around 0.866667</output>

<gadget id="calculator">90 * (13/15)</gadget>
<output>78</output>

<gadget id="calculator">(2/15) / 78</gadget>
<output>1/585 = around 0.001709</output>

<gadget id="calculator">90 * (1/585)</gadget>
<output>2/13 = around 0.153846</output>

<result>2/13 = around 0.153846</result>