Fill in the blank space for the given series with the correct alternative.
$1, 2, 3, 6, 9, 18, (\ldots), 54$

Study the following arrangement carefully and answer the question.
$O, 4, E, J, 5, T, 1, A, M, Q, 3, 8, N, I, K, 7, W, F, 6, S, 9, U, 2, Y, X$
How many such numbers are there in the above arrangement,each of which is immediately preceded by a consonant and also immediately followed by a consonant?

Fill in the blank space for the given series with the correct alternative.
$2, 3, 8, 63, (\ldots)$

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

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

What should come in place of the question mark $(?)$ in the following series based on the above arrangement?

$QP@,MAH,@YZ,?$

Choose the correct alternative to fill in the blanks in the series: $...,...aba..., ...ba ...ab$

If $2$ is subtracted from each odd digit and $3$ is added to each even digit in the number $3675249$,how many digits will appear twice in the new number thus formed?