Find the missing letters for the given series from the given alternatives:
$aaa....bb....aab.....baaa....bb$

Study of the following arrangement carefully and answer the questions given below.

$Q,E ,* ,P,M ,8 ,R,A ,@ ,C ,9 ,U,H,W, \# ,J,Z, ,S, \beta, Y,N ,5 ,\$ ,G,I,T$

If the first element in the above arrangement exchanges its position with the element in the $26 th$ position and the second with the one in the $25 th$ position and so on, which of the following will be in the tenth position from the left after rearrangement?

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

$6, N,P ,=,@, 7,1 ,\& , R, T, 3, L, ,B, \star, E ,4,\# , 8, G,H ,\$, 5, K,M ,?, 2, D,C$

If all the symbols in the arrangement are deleted, which of the following will be the $4^{th}$ to the left of the $12^{th}$ element from the left end?

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?