SAT Math Multiple Choice Practice Question 21: Answer and Explanation

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Question: 21

21. If the distance from Springfield to Watertown is 13 miles, and the distance from Watertown to Pleasantville is 24 miles, then the distance from Pleasantville to Springfield in miles could not be:

A. 10
B. 12
C. 13
D. 24
E. 36

Correct Answer: A


A. To help you solve this problem, make a quick drawing of the situation. (Remember, the towns don't have to be in a straight line.)

The distance you're interested in is the dotted line. Hey, wait a minute: This diagram is a triangle! Therefore, you can use the triangle inequality, which tells you that the sum of any two sides of a triangle must be greater than the third side. The number 10 doesn't satisfy the inequality because 10 + 13 = 23, which is less than 24, so you have your answer.

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