I think you are in a really good position. Most people have difficulty with verbal, so if your verbal is at a 50, you can definitely raise quant in four weeks. This is what I would do. I would get all of the Manhattan GMAT guides if you don't have them already and go through each guide thoroughly. Do not move on to a new chapter until you understand it completely. Make sure you memorize everything you need to memorize from those chapters. Addtionally, make sure you review the math material regularly. Don't just move on to new information without spending at least two days a week reviewing the material you have gone over previously. Good luck.