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Sequences and Series question

2021 · 1 Sep · Shift 2 · Q36
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  5. /2021 · 1 Sep · Shift 2 · Q36

Sequences and Series question

2021 · 1 Sep · Shift 2 · Q36

JEE MainMathematicsSequences and SeriesMCQ+4 / −1
Let a1, a2, ..........., a21 be an AP such that ∑n=1201anan+1=49\sum\limits_{n = 1}^{20} {{1 \over {{a_n}{a_{n + 1}}}} = {4 \over 9}}n=1∑20​an​an+1​1​=94​. If the sum of this AP is 189, then a6a16 is equal to :
  1. A
    57
  2. B
    72
  3. C
    48
  4. D
    36
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