(1/(2*4))+(1/(4*6))+(1/(6*8))+...+(1/(18*20)).
(1/(2*4))+(1/(4*6))+(1/(6*8))+…+(1/(18*20))．
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

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

<result>9/40 = around 0.225</result>