What is the sum of all the simplest proper fractions whose fraction unit is (1/9).
分数单位是(1/9)的所有最简真分数的和是多少．
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

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

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">(1/9) + (2/9) + (4/9) + (5/9) + (7/9) + (8/9)</gadget>
<output>3</output>

<result>3</result>