Question : If $u{_n}=\frac{1}{n}-\frac{1}{n+1}$, then the value of $u{_1} + u{_2}+u{_3}+u{_4}+u{_5}$ is:
Option 1: $\frac{1}{2}$
Option 2: $\frac{1}{3}$
Option 3: $\frac{2}{5}$
Option 4: $\frac{5}{6}$
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Correct Answer: $\frac{5}{6}$
Solution :
Given:
$u{_n}=\frac{1}{n}-\frac{1}{n+1}$
We have to find the value of $u{_1} + u{_2}+u{_3}+u{_4}+u{_5}$.
$u{_1}=1-\frac{1}{2}$
$u{_2}=\frac{1}{2}-\frac{1}{3}$
$u{_3}=\frac{1}{3}-\frac{1}{4}$
$u{_4}=\frac{1}{4}-\frac{1}{5}$
$u{_5}=\frac{1}{5}-\frac{1}{6}$
Now, $ u{_1} + u{_2}+u{_3}+u{_4}+u{_5} = 1-\frac{1}{2} + \frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}$
$=1-\frac{1}{6} =\frac{5}{6}$
Hence, the correct answer is $\frac{5}{6}$.
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