Define a new calculation: a*b=((a*b)/(a+b)) (a, b are both positive integers), then 4*3=how much.
规定一种新的运算：a*b=((a*b)/(a+b))(a，b都是正整数)，则4*3=多少．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">12 / 7</gadget>
<output>12/7 = around 1.714286</output>

<result>12/7 = around 1.714286</result>