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CMA Foundation · Fundamentals of Business Mathematics and Statistics · Arithmetic Progression and Geometric Progression

In a GP, the third term is 18 and the sixth term is 486. What is the first term?

The first term is 2. Dividing the sixth term by the third gives r cubed = 486/18 = 27, so r = 3. The third term is a times r squared = 9a = 18, so a = 2. The series 2, 6, 18, 54, 162, 486 confirms it.

  1. A3
  2. B2Correct
  3. C6
  4. D9

Explanation

Divide the sixth term by the third: ar^5 / ar^2 = r^3 = 486/18 = 27, so r = 3. Then a*r^2 = 18 gives a*9 = 18, so a = 2. Check: 2, 6, 18, 54, 162, 486. Option 6 would be the second term, not the first.

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