Use the symbol "¤" to represent a new operation, and stipulate: a¤b=((ab)/(a+b)). Then, (1/2) ¤ (1/5) = how much.
用符号"¤"表示一种新的运算，并规定：a¤b=((a-b)/(a+b))．那么，(1/2)¤(1/5)=多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/2) + (1/5)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">(3/10) / (7/10)</gadget>
<output>3/7 = around 0.428571</output>

<result>3/7 = around 0.428571</result>