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I found this question on one of the MGMAT CATs and am very confused about their explanation.
The question is as follows: What is the distance between x and y on the number line?
(1) |x| – |y| = 5 (2) |x| + |y| = 11
Here is their explanation:
1) This tells us that the difference between the absolute value of x and the absolute value of y is 5. Let’s pick some numbers to prove that this is insufficient. Say, for example, x = 6 and y = 1. Then |x| – |y| = 5 and the distance between x and y is 6 – 1 = 5. However, let’s pick x = 6 and y = -1. Then |x| – |y| = 5 and the distance between x and y is 6 – (-1) = 7. Since we picked two sets of numbers that fit the criteria and got different answers, the statement is insufficient.
If we pick x = 6 and y = -1, then isn't |x| = 6 and |y| = 1?? Absolute value implies taking the difference from that number and 0, hence it'll always be positive. If we pick x = 6 and y = -1, why are we doing the following operation: 6 - (-1) and not 6 - 1??
Obviously, I am aware that if we draw these two points on the number line, we do indeed get a difference of 7 if y = -1 and x = 6. But could someone explain this algebraically or theoretically why if we pick y = -1 we input the minus sign inside the modulus?
Thanks!
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I found this question on one of the MGMAT CATs and am very confused about their explanation.
The question is as follows: What is the distance between x and y on the number line?
(1) |x| – |y| = 5 (2) |x| + |y| = 11
Here is their explanation:
1) This tells us that the difference between the absolute value of x and the absolute value of y is 5. Let’s pick some numbers to prove that this is insufficient. Say, for example, x = 6 and y = 1. Then |x| – |y| = 5 and the distance between x and y is 6 – 1 = 5. However, let’s pick x = 6 and y = -1. Then |x| – |y| = 5 and the distance between x and y is 6 – (-1) = 7. Since we picked two sets of numbers that fit the criteria and got different answers, the statement is insufficient.
If we pick x = 6 and y = -1, then isn't |x| = 6 and |y| = 1?? Absolute value implies taking the difference from that number and 0, hence it'll always be positive. If we pick x = 6 and y = -1, why are we doing the following operation: 6 - (-1) and not 6 - 1??
Obviously, I am aware that if we draw these two points on the number line, we do indeed get a difference of 7 if y = -1 and x = 6. But could someone explain this algebraically or theoretically why if we pick y = -1 we input the minus sign inside the modulus?
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.