Which particular book should I buy to practice only maths for IIM Indore IPM?

Maths is comparatively tougher than the other two in the IPM aptitude test. So it is important that you prepare for it very thoroughly. The following are some books that are recommended.

Arun Sharma for CAT is an excellent book for practicing math skills. Just remember to quit when it becomes too much, otherwise, you'll end up squandering your time on just one subject. 

Do not attempt any of the higher-level questions in it. But remember this book does not serve as a bible or anything and you’ll have to work very hard to crack this particular exam.

Besides, there is another book named “Word Power Made Easy” which is an excellent English textbook that is also enjoyable to read.