For a simple fraction, add a number to the numerator, the fraction is equal to (4/7), and subtract the same number from the numerator, the fraction is equal to (5/14). What is the simplest fraction?
一个最简分数，分子加上一个数，这个分数就等于(4/7)，分子减去同一个数，这个分数就等于(5/14)．这个最简分数是多少？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">5 / 14</gadget>
<output>5/14 = around 0.357143</output>

<gadget id="calculator">(4/7) + (5/14)</gadget>
<output>13/14 = around 0.928571</output>

<gadget id="calculator">(13/14) / 2</gadget>
<output>13/28 = around 0.464286</output>

<result>13/28 = around 0.464286</result>