1/2+1/6+1/12+1/20.+1/380
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1/2+1/6+1/12+1/20.+1/3801/2+1/6+1/12+1/20.+1/3801/2+1/6+1/12+1/20.+1/3801/2+1/6+1/12+1/20.+1/380=1/(
1/2+1/6+1/12+1/20.+1/380
1/2+1/6+1/12+1/20.+1/380
1/2+1/6+1/12+1/20.+1/380
1/2+1/6+1/12+1/20.+1/380
=1/(1*2)+1/(2*3)+1/)3*4)+...+1/(19*20)
=1-1/2+1/2-1/3+1/3-1/4+...+1/19-1/20
=1-1/20
=19/20
1/2=1/1-1/2
1/6=1/2-1-3
1/12=1/3-1/4
……
1/380=1/19-1/20
1/2+1/6+1/12+1/20.....+1/380=/1-1/2
+1/2-1-3……+1/19-1/20=1-1/20=0.95
1/2+1/6+1/12+1/20.....+1/380
=1/1-1/2+1/2-1/3+1/3-1/4+...+1/19-1/20
=1-1/20
=19/20
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