Fill in the blank space for the given series with the correct alternative.
$6, 15, (\ldots), 45, 66, 91$

How many such digits are there in the number $52361984$ each of which is as far away from the beginning of the number as when the digits are rearranged in ascending order within the number?

To answer these questions study carefully the following arrangement of letters, digits and symbols.

$6,=, C,E, 3,8 ,G,L,M, 7, \star, @ ,P,R, 4, \#, \$, N,T, 5, S,V$

How many such digits are there in the arrangement each of which is immediately preceded by a letter?

Study the following arrangement carefully and answer the questions given below:
$R, 4, E, J, 5, T, 1, A, M, Q, 3, 8, N, I, K, 7, W, F, 6, D, 9, U, 2, Y, V$
Four of the following five are alike in a certain way based on their positions in the above arrangement and so form a group. Which is the one that does not belong to this group?

Choose the correct alternative to complete the series: $a . b e . . c . . a b b . . . b c a . . . .$

Which one of the following is the correct order of missing letters in the series given below?
$....sttt...tt...tts....$