There is a fraction, which can be reduced to (1/4) after adding 1 to the numerator, and can be simplified to (1/5) after subtracting 1 from the denominator. What is the original fraction?
有一个分数，分子加1以后可化简为(1/4)，分母减去1以后可化简为(1/5)，原来这个分数是多少．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">3 / 16</gadget>
<output>3/16 = around 0.1875</output>

<result>3/16 = around 0.1875</result>