Calculation: (1/(5*6))+(1/(6*7))+(1/(7*8))+…+(1/(18*19))+(1/(19* 20)).
计算：(1/(5*6))+(1/(6*7))+(1/(7*8))+…+(1/(18*19))+(1/(19*20))．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/5) - (1/20)</gadget>
<output>3/20 = around 0.15</output>

<result>3/20 = around 0.15</result>