Calculation: (4/(1*6))+(4/(6*11))+(4/(11*16))+…+(4/(71*76))+(4/(76* 81)).
计算：(4/(1*6))+(4/(6*11))+(4/(11*16))+…+(4/(71*76))+(4/(76*81))．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 81</gadget>
<output>1/81 = around 0.012346</output>

<gadget id="calculator">1 - (1/81)</gadget>
<output>80/81 = around 0.987654</output>

<gadget id="calculator">4 * (1/5) * (80/81)</gadget>
<output>64/81 = around 0.790123</output>

<result>64/81 = around 0.790123</result>