Why do this poblem?
This problem calls for interpreting the given data in terms of concepts of probability and, at each stage, reviewing how the weather situation is related to the results of the calculations from the formulae. It provides a good exercise in conditional probability and an opportunity to investigate iteration and a limiting process.

Possible approach
The scaffolding given in the problem itself should be sufficient for most learners to do this problem independently.

Key question
We are given information about the probability that tomorrow is wet. What does this tell us about the probability that tomorrow is dry?

Possible extension
Try the problem FA Cup.

Possible support
The question itself gives a lot of guidance.