How can I lose 40 to 50 pounds in a week and a half?

Not do-able. As my colleague said elsewhere, perhaps by liposuction -- but without an overall nutrition and exercise plan this would not be healthy or wise. Why the hurry?
Make it 20 weeks. Make sure you exercise at least 90 minutes a day, don't skip meals, avoid soda, juice, dairy, alcohol and fried foods. Eat a healthy well balanced diet! Also water, organic vegetable broth, green leafy vegetables, natural pickles, apples are great to fill you up so you dont feel hungry and they are very low in calories.