(4/(1*5))+(4/(5*9))+(4/(9*13))+(4/(13*17))+(4/(17*21))= How many.
(4/(1*5))+(4/(5*9))+(4/(9*13))+(4/(13*17))+(4/(17*21))=多少．
<gadget id="calculator">1 * 5</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">5 * 9</gadget>
<output>45</output>

<gadget id="calculator">4 / 45</gadget>
<output>4/45 = around 0.088889</output>

<gadget id="calculator">9 * 13</gadget>
<output>117</output>

<gadget id="calculator">4 / 117</gadget>
<output>4/117 = around 0.034188</output>

<gadget id="calculator">13 * 17</gadget>
<output>221</output>

<gadget id="calculator">4 / 221</gadget>
<output>4/221 = around 0.0181</output>

<gadget id="calculator">17 * 21</gadget>
<output>357</output>

<gadget id="calculator">4 / 357</gadget>
<output>4/357 = around 0.011204</output>

<gadget id="calculator">(4/5) + (4/45) + (4/117) + (4/221) + (4/357)</gadget>
<output>20/21 = around 0.952381</output>

<result>20/21 = around 0.952381</result>