Is this a simple or a compound sentence?

Question

I was reading an article about types of sentences. It seemed very easy to understand simple and compounds at first, but there is something wrong with the examples! Please read the following sentence:

Mary and Samantha arrived at the bus station early but waited until noon for the bus.

As you can see there is a coordinative conjunction "but" in this sentence and I belive that this is compound. But in the written text it was classified as a simple sentence! The writer mentioned that "arrived" and "waited" is a compound verb, while the whole sentence is considered to be a simple sentence.

Answer 1

Mary and Samantha arrived at the bus station early but waited until noon for the bus.

This is a simple sentence with a compound subject and a compound predicate. It is not a compound sentence because there is only one independent clause.

Answer 2

Mary and Samantha [arrived at the bus station early] but [waited until noon for the bus].

"Mary and Samantha is the subject. The bracketed elements are a coordination of verb phrases, which together with the coordinator "but" form the predicate of the sentence.

There is only one independent clause, the sentence as a whole, and hence this qualifies as a simple sentence.