Question:y gt 2x^2 - 5For which of the following tables are all the values of x and their corresponding values...
GMAT Algebra : (Alg) Questions
\(\mathrm{y \gt 2x^2 - 5}\)
For which of the following tables are all the values of x and their corresponding values of y solutions to the given inequality?
| x | y |
|---|---|
| -2 | 4 |
| 0 | -4 |
| 3 | 14 |
| x | y |
|---|---|
| -2 | 2 |
| 0 | -4 |
| 3 | 10 |
| x | y |
|---|---|
| -2 | 3 |
| 0 | -5 |
| 3 | 13 |
| x | y |
|---|---|
| -2 | 0 |
| 0 | 1 |
| 3 | 15 |
1. INFER the problem requirements
- Given: The inequality \(\mathrm{y \gt 2x² - 5}\)
- Need: A table where ALL coordinate pairs (x, y) satisfy this inequality
- Strategy: Test every single pair in each table - if even one fails, that table is wrong
2. SIMPLIFY each coordinate pair systematically
Starting with Table A, test each pair:
For (-2, 4):
- Substitute: \(\mathrm{4 \gt 2(-2)² - 5}\)
- SIMPLIFY: \(\mathrm{4 \gt 2(4) - 5}\) → \(\mathrm{4 \gt 8 - 5}\) → \(\mathrm{4 \gt 3}\) ✓
For (0, -4):
- Substitute: \(\mathrm{-4 \gt 2(0)² - 5}\)
- SIMPLIFY: \(\mathrm{-4 \gt 0 - 5}\) → \(\mathrm{-4 \gt -5}\) ✓
For (3, 14):
- Substitute: \(\mathrm{14 \gt 2(3)² - 5}\)
- SIMPLIFY: \(\mathrm{14 \gt 2(9) - 5}\) → \(\mathrm{14 \gt 18 - 5}\) → \(\mathrm{14 \gt 13}\) ✓
3. CONSIDER ALL CASES in Table A
All three pairs work! But let me verify the other tables fail by testing their first points:
- Table B: \(\mathrm{2 \gt 2(-2)² - 5}\) → \(\mathrm{2 \gt 3}\) ✗
- Table C: \(\mathrm{3 \gt 2(-2)² - 5}\) → \(\mathrm{3 \gt 3}\) ✗ (equal, not greater)
- Table D: \(\mathrm{0 \gt 2(-2)² - 5}\) → \(\mathrm{0 \gt 3}\) ✗
Answer: A
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak INFER reasoning: Students test only one or two coordinate pairs from a table instead of checking ALL pairs systematically. They might test the first pair in Table A, see it works, and immediately choose A without verifying the other pairs.
This incomplete checking could lead them to accidentally select a wrong table if they happened to test a "working" pair from an otherwise incorrect table, or miss that Table A actually works completely.
Second Most Common Error:
Poor SIMPLIFY execution: Students make calculation errors when evaluating \(\mathrm{2x² - 5}\), especially with negative values or order of operations. For example, calculating \(\mathrm{2(-2)²}\) as -8 instead of +8, or forgetting to square before multiplying by 2.
This may lead them to incorrectly reject the right answer Choice A or incorrectly accept a wrong choice.
The Bottom Line:
This problem requires methodical verification - you must check EVERY coordinate pair in a table, and you must be precise with your algebraic calculations. Rushing through either step will likely lead to the wrong answer.
| x | y |
|---|---|
| -2 | 4 |
| 0 | -4 |
| 3 | 14 |
| x | y |
|---|---|
| -2 | 2 |
| 0 | -4 |
| 3 | 10 |
| x | y |
|---|---|
| -2 | 3 |
| 0 | -5 |
| 3 | 13 |
| x | y |
|---|---|
| -2 | 0 |
| 0 | 1 |
| 3 | 15 |