A series is given with one term missing. Choose the correct option from the given options and complete the series.
5, 6, 9, 15, ?, 40

Select the term that will complete the following letter series.
QN, RP, TS, WW, ___ FH

A series is given with one term missing. Select the correct alternative from the given ones that will complete the series.

PON, LKJ, GFE, ?

Select the option that will fill in the blank and complete the given series.
CDZ, DGE, EJJ, FMO, GPT___

A series is given with one term missing. Select the correct alternative from the given ones that will complete the series.

RS, ZA, HI, ?

A series is given with one term missing. Choose the correct option from the given ones that will complete the series.

2 : 7 : 4 : 9 : ?

2, 10, 30, 68, ?

Which of the following numbers will replace the question mark (?) in the given series?
 17, 20, 60, 64, 256, 261, 1305, ?