1/(5x8) + 1/(8x11) + 1/(11x14) + 1/(14x17) + 1/(17x20)

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1/(5x8) + 1/(8x11) + 1/(11x14) + 1/(14x17) + 1/(17x20)

1/(5x8) + 1/(8x11) + 1/(11x14) + 1/(14x17) + 1/(17x20)
1/(5x8) + 1/(8x11) + 1/(11x14) + 1/(14x17) + 1/(17x20)

1/(5x8) + 1/(8x11) + 1/(11x14) + 1/(14x17) + 1/(17x20)
= 1/3(1/5 - 1/8 +1/8 - 1/11 + 1/11 - 1/14 + 1/14 - 1/17 + 1/17 - 1/20) = 1/3(1/5 - 1/20) = 1/20