GMAT Club Official Explanation:
What is the median of all values of x which satisfy \(|x − 2| = |x − 4| + |x − 6|\)?A. 2
B. 4
C. 5
D. 6
E. 8
The critical points (aka key points or transition points) are 2, 4, and 6 (the values of \(x\) for which the expressions in the absolute values become 0).
So, we should consider the following four ranges:
If \(x < 2\), then:
\(x - 2 < 0\), and thus \(|x - 2| = -(x - 2)\);
\(x - 4 < 0\), and thus \(|x - 4| = -(x - 4)\);
\(x - 6 < 0\), and thus \(|x - 6| = -(x - 6)\).
Hence, in this range \(|x − 2| = |x − 4| + |x − 6|\) becomes \(-(x − 2) = -(x − 4) - (x − 6)\). This gives \(x = 8\). Since this value is out of the range we consider, then for this range the given equation does not have a solution.
If \(2 \leq x < 4\), then:
\(x - 2 \geq 0\), and thus \(|x - 2| = x - 2\);
\(x - 4 < 0\), and thus \(|x - 4| = -(x - 4)\);
\(x - 6 < 0\), and thus \(|x - 6| = -(x - 6)\).
Hence, in this range \(|x − 2| = |x − 4| + |x − 6|\) becomes \(x − 2 = -(x − 4) - (x − 6)\). This gives \(x = 4\). Since this value is out of the range we consider, then for this range the given equation does not have a solution.
If \(4 \leq x < 6\), then:
\(x - 2 \geq 0\), and thus \(|x - 2| = x - 2\);
\(x - 4 \geq 0\), and thus \(|x - 4| = x - 4\);
\(x - 6 < 0\), and thus \(|x - 6| = -(x - 6)\).
Hence, in this range \(|x − 2| = |x − 4| + |x − 6|\) becomes \(x − 2 = x − 4 - (x − 6)\). This gives \(x = 4\). Since this value is within the range we consider, then \(x = 4\) is a valid solution.
If \(x \geq 6\), then:
\(x - 2 \geq 0\), and thus \(|x - 2| = x - 2\);
\(x - 4 \geq 0\), and thus \(|x - 4| = x - 4\);
\(x - 6 \geq 0\), and thus \(|x - 6| = x - 6\).
Hence, in this range \(|x − 2| = |x − 4| + |x − 6|\) becomes \(x − 2 = x − 4 + x − 6\). This gives \(x = 8\). Since this value is within the range we consider, then \(x = 8\) is a valid solution.
Therefore, two values satisfy \(|x − 2| = |x − 4| + |x − 6|\), 4 and 8. The median of these values is (4 + 8)/2 = 6.
Answer: D.