BPSC 65th Prelims Exam 15 Oct 2019 Solved Paper

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Question : 16 of 150

Marks: +1, -0

If

S=∑↙{n=1}↖{15}(n+\;{1}/{3})

then the value of

S

is

125
$120+\;{1}/{3}$
$135+\;{1}/{3}$
130
None of the above\/More than one of the above

Solution:

Given

S=∑↙{n=1}↖{15}(n+\;{1}/{3})

From the given equation, we can write as

S=(1+\;{1}/{3})+(2+\;{1}/{3}) . . .(15+\;{1}/{3})

Then,

S=(1+2+3 . . .+15)+(\;{1}/{3} × 15)

We know,

\;{n(n+1)}/{2},(n \;\text " is "\; 15 \;\text " here ")

=(\;{15 × 16}/{2})+(\;{1}/{3} × 15)

\;=120+5=125

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