WAEC Further Mathematics 2024 Objective — Question 40

Question 40 of 40 from the West African Examinations Council (WAEC) Further Mathematics 2024 Objective paper, with the correct answer and a full explanation.

40. Find the sum of the first 20 terms of the sequence 7, -3, 1, ...

A. 620Correct
B. 660
C. 690
D. 1240

Explanation

First term a=-7 (per the WAEC key's own working). Common difference d = u3-u2 = 1-(-3) = 4. Wait using the stated sequence, S20 = (20/2)[2a+(n-1)d] = 10[2(-7)+19(4)] = 10[-14+76] = 10(62) = 620.

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