S=15+16+17+.......+70
[tex]S= \frac{56(70+15)}{2} = \frac{56x85}{2} = \frac{4760}{2} = 2380[/tex]
S=317+318+319+.......+400
[tex]S= \frac{84(400+317)}{2} = \frac{84x717}{2}=42x717=330114[/tex]
S=1+2+3+.......512
[tex]S= \frac{512(512+1)}{2} = \frac{512x513}{2} = \frac{262656}{2} = 131328[/tex]