SAT Math Multiple Choice Question 626: Answer and Explanation

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Question: 626

11. Images

If s, t, u, and v are the coordinates of the indicated points on the number line above, which of the following is greatest?

  • A. |s - v|
  • B. |s - t |
  • C. |s + v|
  • D. |u + v|

Correct Answer: A

Explanation:

A

Algebra (absolute values) MEDIUM-HARD

First, we should notice that each choice can be interpreted as a distance between two points on the number line.

(A) |s - v| = the distance between s and v

(B) |s - t| = the distance between s and t

(C) |s + v| = |s - (-v)| = the distance between s and -v

(D) |u + v| = |u - (-v)| = the distance between u and -v

Thinking this way gives us a very straightforward way to solve the problem without doing any calculation. First we need to locate -v on the number line by just reflecting v over the origin at 0. (Recall that multiplication by -1 is equivalent to reflecting a point on the number line over the origin at 0.) This makes it easy to see the distances the problem is asking us to compare:

Images

Clearly, the greatest of these distances is (A).

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