There are 15 terms in an arithmetic progression. Its first term is 5 and their sum is 390 . middle t

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8. Sequences and Series

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There are $15$ terms in an arithmetic progression. Its first term is $5$ and their sum is $390$. The middle term is

A

$23$

B

$26$

C

$29$

D

$32$

Solution

(b) According to the given condition

$\frac{{15}}{2}[10 + 14 \times d] = 390$

$ \Rightarrow $ $d = 3$

Hence middle term $i.e.$ ${8^{th}}$ term is given by

$5 + 7 \times 3 = 26$.

Standard 11

Mathematics

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