Visitors to an e$-$commerce website arrive at the site in one of four ways: by direct access $($the visitor types the site$$s URL into a browser or clicks on a bookmark$)$; via a link on another website, e$-$mail message, or banner ad; from a paid listing generated by a search engine; or via an organic $($unpaid$)$ listing generated by a search engine.

Engine Ready, an Internet marketing company, randomly selected $27$ U$.$S$.$ e$-$commerce companies from its $500$ clients and studied a total of $18\mathrm{.}7$ million visits over a $2-$year period. For each visit, data were collected on the traffic source. The relative frequency for each traffic$-$source type are shown in the following table. $[$Source: Engine Ready, $$Examining the Role Traffic Source Plays in Visitor Purchase Behavior,$2008.]$