The fifth term of a GP is 81 and first term is 16. Find

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

1. 36
2. 54
3. 24
4. 18

Correct Option: B

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