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JAMB Mathematics 1988 Question 29

Question 29

Progressions

If 7 and 189 are the first and fourth terms of a geometric progression respectively, find the sum of the first three terms of the progression.

  1. A.182
  2. B.91
  3. C.63
  4. D.28.
Show the answer and explanation

Answer: B (91)

Explanation

7r³ = 189, so r³ = 27 and r = 3. The first three terms are 7, 21 and 63, which add up to 91.