Age Word Problems - Math Forum, a Classic Problem from the Ask Dr. Math FAQ
A problem with one variable: Al's father is 45. He is 15 years older than twice Al's age. How old is Al? But what if we can't express all the information in the problem using only one variable? Sometimes we must use two variables to express the given information, which means that we need two equations to solve for these variables.
Math for Kids: A Medieval Adventure in Problem-solving - ThinkQuest Junior
A site designed by two fourth-graders for sharpening math problem-solving skills: students can practice and learn to solve 30 word problems step-by-step (multiple-choice answers with answer pages are provided), or share word problems they've written. Pages on Word Problem Solving Strategies explore multiple step problems logical reasoning, choosing a calculation method, problems with more than one answer, deciding when to estimate, using data from a chart, and more.