There is a fraction, if the denominator is increased by 1, it will become (2/5), if the denominator is decreased by 1, it will become (1/2), what is the original fraction.
有一个分数，如果分母加1就变成(2/5)，如果分母减1就变成(1/2)，这个分数原来是多少．
<gadget id="calculator">2 / 1</gadget>
<output>2</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) + 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">(9/2) / 2</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">1 / (9/4)</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>