There is a fraction, the numerator can be reduced to (1/3) by adding 1, and the numerator can be reduced to (1/5) by subtracting 1. What is the fraction?
有一个分数，分子加1可以约简为(1/3)，分子减1可约简为(1/5)，这个分数是多少．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">(1/3) + (1/5)</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">(8/15) / 2</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>