ECZ 2017 · O-Level Paper 1 — Sequences and Series
For the sequence 25, 22, 19, 16, …, find the sum of the first 20 terms.
- A. −140
- B. 500
- C. −70
- D. 70
Verified working — step 1
Use the sum formula Sn = n2(2a + (n - 1)d) - and expect a small or negative total, since the terms fall below zero partway.The full step-by-step working and final answer, plus the video lesson for this topic, are included with Premium — checked against ECZ marking standards.
Original examination question © Examinations Council of Zambia. Worked solution and commentary © G12 Titan — not to be reproduced without permission.
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