Simple calculation: (3/(2*4))+(3/(4*6))+(3/(6*8))+...(3/(18*20))=how much.
简便计算：(3/(2*4))+(3/(4*6))+(3/(6*8))+…(3/(18*20))=多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) * (9/10)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">3 * (9/40)</gadget>
<output>27/40 = around 0.675</output>

<result>27/40 = around 0.675</result>