"composed of" vs "comprised of". Which is correct?

Comprise means "contain", as in The hotel comprises 150 rooms. In other words, the hotel has or contains 150 rooms for guests. When you use "comprise", you’re talking about all the parts that make up something whole.

The similar-sounding word compose means "make up" as in Many ethnic groups compose our nation.

So, the parts compose the whole, but the whole comprises the parts.

Strict grammarians will never use "comprised of" in a sentence as it's not considered correct, just as "contained of" would be incorrect.

Incorrect: The United States is comprised of fifty states.
Correct: The United States comprises fifty states.