Inductive reasoning is an important domain-general skill for learning science and math, etc. Unfortunately, previous studies have pointed out that students still have many weaknesses, when they do the tasks of inductive reasoning. A web-based environment is designed to train their skills of inductive reasoning. The pedagogy of self-directed experimentation is adopted in the learning environment, in which learners are asked to express one variable as a function of another variable. Two input interfaces are used for the users to input expressions. The control group uses a traditional tool of expressing a dependent variable as a function of an independent variable. The experimental group uses a tool that can generate a new term by addition, subtraction or multiplication of two existing terms of expressions. Some interesting results are reported.