Genuinely good resources to learn fundamental concepts of Arithmetic

Hi, I have been preparing for CAT since June 25 but I am still not confident even with Arithmetic cause I feel I directly got exposed to the CAT level questions through the coaching material. I need to work on my conceptual understanding to solve these problems but with just 60 days left I don't know what resource shall I use. The solutions provided by the institute also seem difficult for me to comprehend because I have been out of touch with maths for around 5 years now. Let me know if there are some good resources for this.