JEE Math Practice Question
Let a1, a2, ..........., a21 be an AP such that $$\sum\limits_{n = 1}^{20} {{1 \over {{a_n}{a_{n + 1}}}} = {4 \over 9}} $$. If the sum of this AP is 189, then a6a16 is equal to :
- A.57
- B.72
- C.48
- D.36
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