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JAMB Mathematics 2011 Question 22

Question 22

Progressions

The second term of a geometric series is 4 while the fourth term is 16. Find the sum of the first five terms.

  1. A.60
  2. B.62
  3. C.54
  4. D.64
Show the answer and explanation

Answer: B (62)

Explanation

ar = 4 and ar3 = 16 give r2 = 4, so r = 2 and a = 2. S5 = 2(25 − 1)/(2 − 1) = 62.