Answer
$3570$
Work Step by Step
I know that $\sum_{k=1}^{n} (k)=\frac{n(n+1)}{2}.$
Hence $\sum_{k=10}^{60} (2k)=\sum_{k=1}^{60} (2k)-\sum_{k=1}^{9} (2k)=2\sum_{k=1}^{60} (k)-2\sum_{k=1}^{9}=2\frac{60(60+1)}{2}-2\frac{9(9+1)}{2}=3660-90=3570$
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