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If 1 ,   a ,   b and 4 are in harmonic progression, then the value of a + b is equal to

Options

  1. A5 4
  2. B10 3
  3. C3 10
  4. D4 5

Correct answer

B. 10 3

Step-by-step solution

1 , 1 a , 1 b , 1 4 are in A.P. Its common difference D = 1 4 - 1 3 = - 1 4 ⇒ 1 a = 1 + - 1 4 = 3 4 ⇒ a = 4 3 1 b = 1 + 2 - 1 4 = 1 2 ⇒ b = 2 ⇒ a + b = 4 3 + 2 = 10 3

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