A flock of birds fell on a tree, the number of birds that flew away for the first time was the rest (2/5), and 28 birds flew away for the second time, the number of birds that flew away twice was more than the original number (9/14 ) is 2 less, how many birds are there in this tree? (column solution)
有一棵树上落一群鸟，第一次飞走的只数是余下的(2/5)，第二次飞走28只，两次飞走的只数比原来的只数的(9/14)少2只，这棵树上原来有鸟多少只？(列式解答)
<gadget id="calculator">28 + 2</gadget>
<output>30</output>

<gadget id="calculator">9 / 14</gadget>
<output>9/14 = around 0.642857</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 + (2/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">(2/5) / (7/5)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(9/14) - (2/7)</gadget>
<output>5/14 = around 0.357143</output>

<gadget id="calculator">30 / (5/14)</gadget>
<output>84</output>

<result>84</result>