Mathematics 9709 · AS & A Level · Series

Series — practice question

The first term in this arithmetic progression is $-20$, and the common difference is $5$.
(a)[2]

Find the total of the first $20$ terms in the progression.

(b)[3]

The sum of the first $2k$ terms is $10$ times the sum of the first $k$ terms. Find the value of $k$.

Worked solution & mark scheme

This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Valid application of $S_{20}$ with $a=-20$, $d=5$” …

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