SAT Math Multiple Choice Practice Question 182: Answer and Explanation

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Question: 182

6. In triangle ABC, side AB is 12 units long and side BC is 15 units long. The length of side AC may not equal

A. 23
B. 24
C. 25
D. 26
E. 27

Correct Answer: E


E. Triangle inequality! Remember that in any triangle, the sum of any two sides must be greater than the length of the third side. (See Chapter 16 to review this idea.) So, adding sides AB and BC, you get 27 units. The third side must be shorter than 27, so Choice (E) is the only answer that's impossible.

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