Genevieve is buying a car audio system that consists of a stereo, speakers, and amplifiers. She is choosing between 5 types of stereos and 2 types of amplifiers. If she has a total of 30 choices, how many types of speakers must there be?

The correct answer for this question is this one: Speakers = 23.

Given the facts presented above,

The car audio system consists of a stereo, speakers, and amplifiers.

She is choosing between 5 types of stereos and 2 types of amplifiers.

If she has a total of 30 choices, then we have

30 = Speakers + Stereos + Amplifiers

30 = Speakers + 5 + 2

30 = Speakers + 7

Speakers = 30 - 7

Speakers = 23.