1/30+1/42+1/56+1/72+1/90

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1/30+1/42+1/56+1/72+1/901/30+1/42+1/56+1/72+1/901/30+1/42+1/56+1/72+1/901/30+1/42+1/56+1/72+1/90=1/(

1/30+1/42+1/56+1/72+1/90
1/30+1/42+1/56+1/72+1/90

1/30+1/42+1/56+1/72+1/90
1/30+1/42+1/56+1/72+1/90
=1/(5*6)+1/(6*7))+1/(7*8)+)+1/(8*9))+1/(9*10)
=(7+5)/(5*6*7)+(9+7)/(7*8*9)+1/(9*10)
=12/(5*6*7)+16/(7*8*9)+1/(9*10)
=2/(5*7)+2/(7*9)+1/(9*10)
=2*(9+5)/(5*7*9)+1/(9*10)
=28/(5*7*9)+1/(9*10)
=4/(5*9)+1/(9*10)
=(8+1)/(9*10)
=1/10