May I know which exam you talking about ?

I would be able to help better if I can know the precise exam that you are referring to.

NRTI Aptitude Test will comprise of100 multiple choice questions, which will be divided into the following four sections:

English Proficiency - 25 questions

Reasoning & General Intelligence - 30 questions

Quantitative & Numerical Ability - 25 questions

General Awareness - 20 questions

Aptitude:R S Agrawal. It depends on your current aptitude level. If you can solve SSC-CHSL level aptitude you can crack it too.

2.English:Wren and Martin, I think will be the best book for English. If you have ample time, please go through it once.

3.General Knowledge(Current Affairs): Most unpredictable thing in this exam. It comprises of mostly static GK from Geography, sports. Try reading newspaper. Download TOI and apps like those which help you to stay updated.

4.Mathematics: Nothing too hard in Mathematics, just the basic knowledge upto 10 class will be enough to crack this exam.