BPSC 64th Prelims Exam 16 Dec 2018 Solved Paper

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Question : 130 of 150

Marks: +1, -0

If

S=∑↙{n=1}↖{10}(2 n+\;{1}/{2}),

then

S

is

$55^{1 / 2}$
56
111
115
$1101 / 2$

Solution:

{S}=∑↙{n=1}↖{10}(2 n+\;{1}/{2})

Then

{S}=∑↙{n=1}↖{10} 2 n+∑↙{n=1}↖{10} \;{1}/{2}

=2 ∑↙{n=1}↖{10} n+10 × \;{1}/{2}

=\;{2(10)(10+1)}/{2}+5

\;\; [

Note:

1+2+3 . . . n=\;{n(n+1)}/{2}]

=110+5=115

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