Each of the 5 instances will register itself with the scan listener (using the instance parameter remote_listener). Thus, the scan listener is "aware" of the database instances on the other two nodes where it is not running. It can still redirect incoming connections to the local listeners on these nodes (registered as local_listener).
Hemant K Chitale
Scan is not configured as per number of cluster nodes, in a cluster there will be only one scan address resolving to three different ip's for high avaliability purpose. So even in 10 or 20 node cluster, there will be only one scan address (listining on three different ip's), it will be running on any availiable cluster nodes and listens for connections.