JAMB Mathematics 2025 Objective — Question 8
Question 8 of 40 from the Joint Admissions and Matriculation Board (JAMB) Mathematics 2025 Objective paper, with the correct answer and a full explanation.
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Find the sum of the series: 5+10+20+...+1280.
- A. 2555Correct
- B. 3050
- C. 3400
- D. 2570
Explanation
GP with a=5, r=2. 5×2^(n-1)=1280 ⇒ n=9. Sn = 5(2⁹-1)/(2-1) = 5×511 = 2555.
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