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The fifth term of a GP is 81 and first term is 16. Find the 4th term.?

Correct Answer: 54

Explanation:

The nth term of a GP is arn - 1 ,
5th term = ar5 - 1 = ar4 = 81
1st term = a = 16
∴ r4 = 81/16
⇒ r = ∜81/16 = 3/2
∴ 4th term = ar4 - 1 = ar3 = 16 x 3/2 x 3/2 x 3/2 = 54


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