Subtract 2 from the denominator of a fraction to get (4/5). If you add 1 to its denominator, you get (2/3), what is the fraction.
将一个分数的分母减去2得(4/5)．如果将它的分母加上1，则得(2/3)，这个分数是多少．
<gadget id="calculator">2 + 15</gadget>
<output>17</output>

<gadget id="calculator">12 / 17</gadget>
<output>12/17 = around 0.705882</output>

<result>12/17 = around 0.705882</result>