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If the sum of an infinite GP be 9 and sum of first two terms be 5 then their common ratio is …..

Options

  1. A1 3
  2. B3
  3. C2 3
  4. D3 2

Correct answer

C. 2 3

Step-by-step solution

We have, Sum of infinite GP, a 1 - r = 9 ⇒ a + a r = 5 ⇒ a 1 + r = 5 ⇒ 9 1 - r 1 + r = 5 ⇒ 1 - r 2 = 5 9 ⇒ r 2 = 4 9 ⇒ r = 2 3

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