Calculation: (1/(11*13))+(1/(13*15))+(1/(15*17))+(1/(17*19)).
计算：(1/(11*13))+(1/(13*15))+(1/(15*17))+(1/(17*19))．
<gadget id="calculator">11 * 13</gadget>
<output>143</output>

<gadget id="calculator">1 / 143</gadget>
<output>1/143 = around 0.006993</output>

<gadget id="calculator">13 * 15</gadget>
<output>195</output>

<gadget id="calculator">1 / 195</gadget>
<output>1/195 = around 0.005128</output>

<gadget id="calculator">15 * 17</gadget>
<output>255</output>

<gadget id="calculator">1 / 255</gadget>
<output>1/255 = around 0.003922</output>

<gadget id="calculator">17 * 19</gadget>
<output>323</output>

<gadget id="calculator">1 / 323</gadget>
<output>1/323 = around 0.003096</output>

<gadget id="calculator">(1/143) + (1/195) + (1/255) + (1/323)</gadget>
<output>4/209 = around 0.019139</output>

<result>4/209 = around 0.019139</result>