There are several instances where people who are weak in maths have cleared CAT but you will have to definitely work very hard for it. Practice every single day. First focus on clearing the basics of the various topics that are important for CAT and then move to the advanced level. Try taking as many mocks and sectional tests as possible. I would recommend you to join a coaching which will help you to get hold of the concepts. You can also follow books - Quantum CAT by Sarvesh Verma and Quantitative Aptitude for CAT by Arun Sharma. Thanks!