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
Sₙ = n2[2a + (n − 1)d] = 202[2(25) + 19(−3)] = 10(50 − 57) = …The full step-by-step working and final answer 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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