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Find the sum of all integers between $50$ and $500$, which are divisible by $7$.
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$56, 63, ..., 497$
Here $a = 56$ and $d=7$
Let $a_n = 497$
$\Rightarrow 56 + (n-1) \times 7 = 497$
$\Rightarrow n = 64$
$S_{64} = \frac{64}{2} \times (56 + 497) = 17696$
Here $a = 56$ and $d=7$
Let $a_n = 497$
$\Rightarrow 56 + (n-1) \times 7 = 497$
$\Rightarrow n = 64$
$S_{64} = \frac{64}{2} \times (56 + 497) = 17696$