What is the efficient markets hypothesis?

1. What is the difference between adaptive expectations and rational expectations?
2. What is the efficient markets hypothesis?
3. According to the efficient markets hypothesis, are stock prices predictable? What is a random walk?
4. Suppose that you buy an Apple iPad, you like it, and you think it will be a big seller. You expect that Apple’s profits will increase tremendously as a result of booming iPad sales. Should you invest in Apple?