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JAMB Mathematics 2009 Question 18

Question 18

Progressions

The sum of the first n terms of the arithmetic progression 5, 11, 17, 23, 29, 35, ... is

  1. A.n(3n − 0.5)
  2. B.n(3n + 2)
  3. C.n(3n + 2.5)
  4. D.n(3n + 5)
Show the answer and explanation

Answer: B (n(3n + 2))

Explanation

a = 5 and d = 6, so Sn = n/2 [10 + 6(n − 1)] = n/2 (6n + 4) = n(3n + 2).