JEE Mathematics · Medium

Sequences and Series: Inserting means MCQ

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Inserting meansMediumQuestion 210011

Question

The number of arithmetic means between 2 and 26 so that the ratio of 7th and 2nd means is 5:2 is:
  1. A
    15
    Correct
  2. B
    8
  3. C
    9
  4. D
    10

Correct answer

15

Explanation

If the common difference is d, (2+7d)/(2+2d)=5/2(2+7d)/(2+2d)=5/2 gives d=3/2d=3/2. Also d=(26−2)/(n+1)=24/(n+1)d=(26-2)/(n+1)=24/(n+1), so n+1=16n+1=16 and n=15.