Let Sa denote the sum of first n terms an arithmetic progression. If S20=790 and S10=145, then S15- S5 is :

Question

Let

S_{a}

denote the sum of first

n

terms an arithmetic progression. If

S_{20} = 790

and

S_{10} = 145

, then

S_{15} -

S_{5}

is :

395

390

405

410

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