Let's think about what this question is really asking: You have x numbers, and you want to know: by what percent is their SUM greater than their AVERAGE?
Here's the key insight you need to see: there's a fundamental relationship between sum and average that makes this problem work beautifully.
Step 1: Establish the Sum-Average RelationshipLet's call the average of your x numbers "A". Now, remember how averages work:
Average = Sum ÷ Number of values
So if we flip this around:
Sum = Average × Number of values
Sum = \(A \times x\)
Notice that we now have both the sum and average expressed in terms of A.
Step 2: Find the DifferenceHow much greater is the sum than the average?
Difference = Sum - Average
Difference = \((A \times x) - A\)
Difference = \(A(x - 1)\)
Let's test this with real numbers to make sure it makes sense. Say you have 3 test scores: 80, 90, and 100.
- Sum = 270
- Average = 90
- Difference = 270 - 90 = 180
Using our formula: \(A(x-1) = 90(3-1) = 90(2) = 180\) ✓
Step 3: Convert to PercentageHere's where you need to be careful. The question asks "what percent GREATER THAN" - this means we need the percent increase formula:
\(Percent\ increase = \frac{Difference}{Original} \times 100\%\)
What are we comparing to? The average. So:
\(Percent\ increase = \frac{A(x-1)}{A} \times 100\%\)
Notice how the A's cancel out:
\(= (x-1) \times 100\%\)
\(= 100(x-1)\%\)
Step 4: VerifyLet's check with our example (3 test scores, sum = 270, average = 90):
Using our formula: \(100(3-1)\% = 100(2)\% = 200\%\)
Direct calculation: \(\frac{270-90}{90} \times 100\% = \frac{180}{90} \times 100\% = 200\%\) ✓
Answer: E - 100(x-1)%The beautiful thing about this result is that it doesn't matter what the actual numbers are or what the average is - the percent increase only depends on HOW MANY numbers you have (x).
Want to master this question type?While you've got the core solution here, there's something really valuable about understanding WHY this pattern emerges and how to recognize similar structures in other GMAT problems. The complete solution on Neuron breaks down the systematic framework for all "percent greater than" problems and shows you the exact traps to avoid (like confusing "percent greater than" with "percent of" - which trips up many students at the answer choice stage!).
You can check out the
detailed step-by-step solution on Neuron to see the smart numbers alternative approach (which can be faster for some students) and learn the broader patterns that apply to similar questions. You can also practice with comprehensive explanations for
other official questions on Neuron to build systematic accuracy across all question types.