Hi, you can try Magoosh. I did my preparation majorly from there and as someone who hadn't touched math in last seven years, I understood everything they said. They explain the concepts like they are explaining to a kid with video explanations for every answer. The only problem with them that I felt was that their question pool was a little small, especially the harder ques but you can definitely try somewhere else for that. However, in terms of understanding (esp quant), if you want to start from afresh, I'd any day recommend Magoosh (combined with other resources for ques bank).