A minimal fraction, if 1 is added to the numerator, it can be reduced to (4/5), and if 1 is subtracted from the numerator, it can be reduced to (2/3). What is the simplest fraction?
一个最简分数，若分子加上1，可以约简为(4/5)，若分子减去1，可以约简为(2/3)，这个最简分数是多少？
<gadget id="calculator">11 / 15</gadget>
<output>11/15 = around 0.733333</output>

<result>11/15 = around 0.733333</result>