Angie$$s List provides three tiers of services: Green, Sliver, and Gold. Customers can access the Green service for free. The Sliver service charges customers $$24\mathrm{.}99$ per year. $$99\mathrm{.}99$ is the annual price for the Gold service. A market research shows that $50\%$ of subjects are willing to choose the Green service, $30\%$ of subjects are willing to choose the Sliver service, and $20\%$ of subjects prefer the Gold service. What is the average revenue that Angie$$s List can make from one customer?

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