Prince first you should be aware of syllabus and number of questions will be asked in MAT exam. There will be 40 each questions. As you know, Gk is divided into two sections. 

1.Static GK 

Consists of areas that do not change over time. Questions related to history, companies and brand, geography, headquarters, sports, political system and miscellaneous cover in this. 

While the syllabus seems to be very vast, you can prepare from reliable sources like" India 2015 " which is popularly known as" India year book ". This book can be dowdownload for free as well. Further you may refer to the www.pib.nic.in. 

2. Current Gk

This includes questions regarding daily updates. For this you should read daily news paper other than books. You may prepare current affairs of the last 12 months from any reputated competition specific magazine like Pratiyogita darpan, Sucess review etc. You can also download app like Grade up, Hittsbull eye etc as these provide daily Gk updates.