This chapter of the HyperStat Online Textbook presents six sections on probability including conditional probability, unions, intersections, and the Binomial distribution. A link to exercises for the chapter is available, as well as a link to an applet that demonstrates the approximation of the binomial with a normal distribution (in section 5).
Gives four practice problems on the t-test. Gives both the data sets and the mean and standard deviations if you did not want to compute them. Requires students to interpret and reason through some of their answers.