Verbal Reasoning - Mental Ability Questions

In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?
a _ bc _ a _ bcdabc _ da _ cd _

A series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.

0, 3, 8, ? , 24, 35

The weights of 4 boxes are 30, 40, 50 and 100 kilograms. Which of the following cannot be the total weight, in kilograms, of any combination of these boxes and in a combination a box can be used only once?

A series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.
6, 18, 54, ? , 486, 1458

In the following question, select the related letter pair from the given alternatives.PIR : OHQ : : ? : ?

P is the brother of Q. Q is the brother of R. P is the son of S. Based these three statements, much of the following statements cannot be definitely true?

In each of the following questions three statements are given and these statements are followed by two conclusions numbered (1) and (2). You have to take the given three statements to be true even if they seem to be at variance from commonly known facts. Read the conclusions and then decide which of the given conclusions logically follows from the two given statements, disregarding commonly known facts.
Statements:

All books are novels.
No novel is a magazine.
All magazines are newspaper.
Conclusions: 

I.No book is a magazine.
II. Some newspaper are novels.

A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.

?, ONM, GFE, XWV