## anonymous one year ago Find S25 for 3+7+11+15

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1. anonymous

Let $$a_1=3$$, $$d=7-3=4$$ and $$n=25$$. Since this is an arithmetic series, we have $S_{25}=\frac{n}{2}[2a_1+(n-1)d]=\frac{25}{2}[2(3)+(25-1)4]=\boxed{1275}$