Set S consists of five consecutive integers, and set T consists of seven consecutive integers. Is the median of the...
GMAT Data Sufficiency : (DS) Questions
Set S consists of five consecutive integers, and set T consists of seven consecutive integers. Is the median of the numbers in set S equal to the median of the numbers in set T?
- The median of the numbers in Set S is 0
- The sum of the numbers in set S is equal to the sum of the numbers in set T
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Understanding the Question
Let's start with what we need to determine: Is the median of set S equal to the median of set T?
Given Information:
- Set S consists of five consecutive integers
- Set T consists of seven consecutive integers
What We Need to Determine:
For consecutive integers, the median is simply the middle value:
- Set S (5 numbers): The median is the 3rd number in the sequence
- Set T (7 numbers): The median is the 4th number in the sequence
Here's the key insight that will unlock this problem: For any set of consecutive integers, the sum equals \(\mathrm{(number\,of\,terms)} \times \mathrm{(median)}\). This means:
- Sum of S = \(5 \times \mathrm{median\,of\,S}\)
- Sum of T = \(7 \times \mathrm{median\,of\,T}\)
This relationship will prove crucial for our analysis.
Analyzing Statement 1
Statement 1: The median of the numbers in Set S is 0
This tells us exactly what the median of S is (which is 0), but gives us absolutely no information about set T. Without knowing anything about T's median, we cannot determine whether it also equals 0.
Let's visualize with examples:
- If T = {-3, -2, -1, 0, 1, 2, 3}, then median of T = 0 → Answer: YES, they're equal
- If T = {2, 3, 4, 5, 6, 7, 8}, then median of T = 5 → Answer: NO, they're not equal
Since we can get both YES and NO answers, Statement 1 is NOT sufficient.
[STOP - Not Sufficient!] This eliminates choices A and D.
Analyzing Statement 2
Now let's forget Statement 1 completely and analyze Statement 2 independently.
Statement 2: The sum of the numbers in set S is equal to the sum of the numbers in set T
Using our key insight from earlier:
- Sum of S = \(5 \times \mathrm{median\,of\,S}\)
- Sum of T = \(7 \times \mathrm{median\,of\,T}\)
If these sums are equal:
\(5 \times \mathrm{median\,of\,S} = 7 \times \mathrm{median\,of\,T}\)
This gives us: median of S = \(\frac{7}{5} \times \mathrm{median\,of\,T}\)
The medians can only be equal when both equal 0! Here's why:
- If median of S = median of T = m (where m ≠ 0)
- Then \(5m = 7m\), which is impossible unless \(m = 0\)
Let's test specific scenarios to confirm:
Scenario | Median of T | Median of S | Calculation | Are they equal? |
Case 1 | 0 | 0 | \(\frac{7}{5} \times 0 = 0\) | YES ✓ |
Case 2 | 5 | 7 | \(\frac{7}{5} \times 5 = 7\) | NO ✗ |
Case 3 | -5 | -7 | \(\frac{7}{5} \times (-5) = -7\) | NO ✗ |
Different scenarios give different answers, so Statement 2 is NOT sufficient.
[STOP - Not Sufficient!] This eliminates choice B.
Combining Statements
Now let's see what happens when we use both statements together.
From Statement 1: The median of S is 0
From Statement 2: Sum of S = Sum of T
Since the median of S is 0:
- Sum of S = \(5 \times 0 = 0\)
Since the sums are equal (from Statement 2):
- Sum of T = 0
Therefore:
- Sum of T = \(7 \times \mathrm{median\,of\,T} = 0\)
- This means: median of T = \(\frac{0}{7} = 0\)
Conclusion: Both medians equal 0, so we can definitively answer YES - the medians are equal.
The statements together are sufficient.
[STOP - Sufficient!] This eliminates choice E.
The Answer: C
Together, the statements tell us that both sets must have median 0, allowing us to answer the question with certainty.
Answer Choice C: "Both statements together are sufficient, but neither statement alone is sufficient."