According to the spec you cannot have an interface that is Remote and Local at the same time. However, you create a super-interface, put all methods there, and then create 2 sub-interfaces. Having done that, simply use @EJB. This way you need to maintain only one interface at all.
EDIT: See section 3.2 in "EJB3 spec simplified" at http://jcp.org/aboutJava/communityprocess/final/jsr220/index.html
Home is responsible for the creation of the Remote (kind of like its constructor) and LocalHome and Local have the same relationship.
In each case the container is giving you a proxy that references the real EJB class that you write.
If I had to guess, what the question was looking for was the use of remote for the session bean and local for the entity bean.
Anyway, although these concepts can still exists, things have been much better simplified in EJB3.
EDIT: In response to the comment, with EJB3, the bean class itself can implement the remote and the home interfaces directly (for the session beans). They are made EJB's with a single annotation. Stateful beans have a couple more annotations to deal with state issues. Entity beans do not have a Home interface, and do not need a local interface, you can interact with the java object directly. There is an EntityManager that retrieves the right entity beans based on a query, and that EntityManager is injected via an annotation.
That kind of sums it up in a paragraph. There are great tutorials on the web for this stuff, but EJBs in general solve a class of problem that is hard to appreciate unless you deal with the problem. They aren't the only way to solve it, but unless you deal with this type of programming, just reading about it won't really help you relate to it.
Best Answer
This is what the EJB spec says:
The choice between the local and the remote programming model is a design decision that the Bean Provider makes when developing the enterprise bean.
While it is possible to provide both a remote client view and a local client view for an enterprise bean, more typically only one or the other will be provided.
JSR220 Chapter 3
So when writing a bean think about who is the client, it's very unlikely that a local client will need the same methods or even the same bean that a remote one.