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 _

In a certain code language, '-' represents 'x', '÷' represents '+', '+' represents '÷' and 'x' represents '-'. Find out the answer to the following question.

23 x 20 ÷ 35 - 2 + 10 = ?

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

FED , IHG , LKJ , ONM, ?

In the following question, select the odd number pair from the given alternatives.

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

XXXXXO, XXXXOX, XXXOXX, XXOXXX, XOXXXX, ?

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

BD, EG, HJ, ?

Choose the related word/letters/number from the given alternatives.
NPR : GHI : : TVX : ?

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

RS, WX, ? , GH