What is the sum of the simplest proper fractions whose unit of fraction is (1/10).
分数单位是(1/10)的最简真分数的和是多少．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(1/10) + (3/10) + (7/10) + (9/10)</gadget>
<output>2</output>

<result>2</result>