Answers for the Challenge Master problems in the Math Expressions textbook series are available on the book publisher's website. Go to EduPlace.com and select your state from the drop-down menu. Click on Mathematics, then choose Math Expressions.
Select the grade level for the particular Math Expressions textbook and click on Teaching Tools. Click on Challenge Masters to see blank worksheets and answer keys.
For help with Math Expressions problems not included in the Challenge Masters worksheets, go to MathWay.com. This website allows users to enter specific math problems ranging from basic elementary school math to college level calculus. Results include both the problem's answer and the step-by-step process for solving the problem.