What letters will fill the blank?

Z, X, V, T, R, __,__

The given number series is 22, 11, 33, 16.5, 49.5, ?

22

22 / 2 = 11

11 x 3 = 33

33 / 2 = 16.5

16.5 x 3 = 49.5

49.5 / 2 = 24.75

Hence, the next number series is 24.75.

The given number series 9, 19, 21, 43, 45, ... follows a pattern that

ALternately (x 2 + 1) and  (x 1 + 2)

9 

9 x 2 + 1 = 19

19 x 1 + 2 = 21

21 x 2 + 1 = 43

43 x 1 + 2 = 45

45 x 2 + 1 = 91

Hence, the next number in the given sequence is 91.

The given number series 999, 990, 998, 991, 997, 992, ?

It follows a pattern that,

999

999 - 9 = 990

990 + 8 = 998

998 - 7 = 991

991 + 6 = 997

997 - 5 = 992

992 + 4 = 996

Hence, the next number in the given number series is 996.

Here the given number series 625, 625, 600, ?, 475, 875 follows a pattern that

625

625 + (0 x 0) = 625

625 - (5 x 5) = 625 - 25 = 600

600 + (10 x 10) = 600 + 100 = 700

700 - (15 x 15) = 700 - 225 = 475

475 + (20 x 20) = 475 + 400 = 875

Hence, the missing number in the given number series is 700.

The given series is 9 81 ? 6561 59049

It follows a pattern that

9

81 = 9 x 9

729 = 9 x 9 x 9

6561 = 9 x 9 x 9 x 9

59049 = 9 x 9 x 9 x 9 x 9

Hence, the missing number in the series is 729.

The given series is 6, 6, 12, 36, 144, 720, ?

6

6 x 1 = 6

6 x 2 = 12

12 x 3 = 36

36 x 4 = 144

144 x 5 = 720

720 x 6 = 4320

Hence, the next number in the given number series is 4320.

The given number series follows a pattern that, 4, 15, 37, 81, ?

4

4 + 11 = 15

15 + 22 = 37

37 + 44 = 81

81 + 88 = 169

Hence, the next number in the sequence is 169.

The given series 404, 415, 402, 413, 400, ? follows a pattern that,

404

404 + 11 = 415

415 - 13 = 402

402 + 11 = 413

413 - 13 = 400

400 + 11 = 411

Hence the next number in the given number series is 411.