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GCE Mathematics 1989 Question 2

Question 2

Progressions

If the second and fourth terms of a G.P. are 8 and 32 respectively, what is the sum of the first four terms?

  1. A.28
  2. B.40
  3. C.48
  4. D.60
  5. E.68.
Show the answer and explanation

Answer: D (60)

Explanation

ar = 8 and ar3 = 32, so r2 = 4, r = 2 and a = 4. The terms are 4, 8, 16, 32, which add up to 60.