Question

\(\dfrac{1}{12}\)+\(\dfrac{1}{20}\)+.....+\(\dfrac{1}{90}\)

Answer 1

TK

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Answer 2

\(=\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{9.10}\)

\(=\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{9}-\dfrac{1}{10}\)

\(=\dfrac{1}{3}-\dfrac{1}{10}=\dfrac{10}{30}-\dfrac{3}{30}=\dfrac{7}{30}\)