Final answer:
The provided sentence is a complex sentence, containing one independent clause and one dependent clause, with the dependent clause beginning with the subordinating conjunction 'Even though.'
Step-by-step explanation:
The sentence "Even though his friends advised against it, he bought the overpriced concert tickets." is a complex sentence.
This is because the sentence is comprised of one independent clause, "he bought the overpriced concert tickets," which can stand alone as a complete sentence, and one dependent clause, "Even though his friends advised against it," which cannot stand alone and is connected to the main clause.
A complex sentence is characterized by the presence of one independent clause and at least one dependent clause. This sentence structure allows the writer to express a nuanced idea that the action took place despite some advice or condition presented in the dependent clause.