Which of the following numbers will replace the question mark (?) in the given series?5, 3, 20, 9, 80, 27, 320, ?

The given series is an alternating series consisting of two distinct geometric/arithmetic sequences:First sequence (at odd positions): 5, 20, 80, 320$5\times 4=20$$20\times 4=80$$80\times 4=320$ Second sequence (at even positions): 3, 9, 27, ?$3\times 3=9$$9\times 3=27$$27\times 3=81$ The question mark occupies an even position (8th term), so it belongs to the second sequence.Therefore, the next number is $27\times 3=81$.