The least common multiple of the numerator and denominator of a fraction is 80. If the numerator is added to 4, it is the smallest improper fraction. If reduced to the simplest fraction, the numerator is 1 less than the denominator. What is the original fraction?
一个分数的分子、分母的最小公倍数是80，如果分子加4，则是一个最小的假分数，如果约成最简分数，则分子比分母少1，原来的分数是多少．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">16 / 20</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>