Passive voice sentences have part of the sentence that does not state the actor. Active voice sentences state the actor. For each sentence, look for an action that has no actor. “Mistakes were made” has no actor. It is in passive voice. “The committee made mistakes” has an actor: the committee. It is in active voice.
Also, if the sentence has the actor after the action, as in “mistakes were made by the committee,” it is still in passive voice. The reason is that active voice has the actor before the action. In your business writing, try to use active voice sentences most of the time.