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The sum of first $15$ terms of an A.P. is $750$ and its first term is $15$. Find its $20^{th}$ term.
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$a = 15, S_{15} = 750$
$\frac{15}{2}[2a + 14d] = 750$
$2(15) + 14d = 100$
$d = 5$
$a_{20} = a + 19d = 15 + 19(5) = 110$
$\text{OR}$
$\frac{15}{2}[2a + 14d] = 750$
$2(15) + 14d = 100$
$d = 5$
$a_{20} = a + 19d = 15 + 19(5) = 110$
$\text{OR}$