Fill in the blank space for the given series with the correct alternative.
$3, 7, 15, 31, 63, (\dots)$

In the series $7, 14, 28, \ldots$,what will be the $10^{th}$ term?

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

Which of the letters will come next in the following series?
$a, ab, abc, abcd, abcde, abcde, ?$

Study carefully the following arrangement of letters,digits,and symbols to answer the question:
$M, 7, \&, 8, L, P, @, Q, N, \beta, T, Y, 3, 2, =, E, 4, 9, \#, G, H, 5$
How many such letters are there in the arrangement,each of which is immediately followed by a number?

Following questions are based on the five three-digit numbers given.
$513, 248, 371, 634, 167$
If the positions of the first and the second digits in each of these numbers are interchanged,which of the following will be the lowest number among them?