Which book is best for clearing concepts?

I started preparing for GMAT a month ago. I am quite week at quant section and also not dat gud in verbal 1. I am taking my classes from an institute in India. But i dont find there material sufficient to clear all concepts. Trainers at my institute dont suggest any other book. Kindly suggest which book shud i buy to do the same which includes all the relevent topics and point as per GMAT and OG.

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