The first thing to do is add a field called Weighted Revenue of type currency to the Opportunity entity as shown.
Now create a business rules that sets the value of the weighted revenue field based on the probability value. In this example we simply multiply the estimated revenue by the probability and divide by 100.
You can now use the weighted revenue in your reports and charts. You should consider using the Weight Revenue (Base) field in your report if you plan to support multiple currencies.