y lt x^2 + 5 For which of the following tables are all the values of x and their corresponding...
GMAT Algebra : (Alg) Questions
\(\mathrm{y \lt x^2 + 5}\)
For which of the following tables are all the values of x and their corresponding values of y solutions to the given inequality?
Choose 1 answer:
| x | y |
|---|---|
| 3 | 14 |
| 5 | 30 |
| 7 | 54 |
| x | y |
|---|---|
| 3 | 10 |
| 5 | 34 |
| 7 | 50 |
| x | y |
|---|---|
| 3 | 10 |
| 5 | 26 |
| 7 | 50 |
| x | y |
|---|---|
| 3 | 18 |
| 5 | 34 |
| 7 | 58 |
1. TRANSLATE the inequality requirement
- Given: \(\mathrm{y \lt x² + 5}\)
- This means: For each (x,y) pair, the y-value must be less than \(\mathrm{x² + 5}\)
- We need ALL pairs in a table to satisfy this condition
2. SIMPLIFY to find the boundary values
- Calculate \(\mathrm{x² + 5}\) for each x-value:
- For \(\mathrm{x = 3}\): \(\mathrm{3² + 5 = 9 + 5 = 14}\)
- For \(\mathrm{x = 5}\): \(\mathrm{5² + 5 = 25 + 5 = 30}\)
- For \(\mathrm{x = 7}\): \(\mathrm{7² + 5 = 49 + 5 = 54}\)
3. CONSIDER ALL CASES by checking each table systematically
Table A:
- (3, 14): Is \(\mathrm{14 \lt 14}\)? No ✗
- Since the first pair fails, Table A is eliminated
Table B:
- (3, 10): Is \(\mathrm{10 \lt 14}\)? Yes ✓
- (5, 34): Is \(\mathrm{34 \lt 30}\)? No ✗
- Since one pair fails, Table B is eliminated
Table C:
- (3, 10): Is \(\mathrm{10 \lt 14}\)? Yes ✓
- (5, 26): Is \(\mathrm{26 \lt 30}\)? Yes ✓
- (7, 50): Is \(\mathrm{50 \lt 54}\)? Yes ✓
- All pairs satisfy the inequality!
Table D:
- (3, 18): Is \(\mathrm{18 \lt 14}\)? No ✗
- Since the first pair fails, Table D is eliminated
Answer: C
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak CONSIDER ALL CASES skill: Students check only the first pair in each table and select based on partial information.
For example, they might check Table A, see that \(\mathrm{14 \lt 14}\) is false, then check Table B, see that \(\mathrm{10 \lt 14}\) is true, and immediately select B without checking the remaining pairs. Since \(\mathrm{34 \lt 30}\) is false, this leads them to select Choice B (Table B).
Second Most Common Error:
Poor TRANSLATE reasoning: Students misinterpret the inequality direction, thinking \(\mathrm{y \gt x² + 5}\) instead of \(\mathrm{y \lt x² + 5}\).
This reversal makes them look for y-values that are greater than the calculated boundary values. Under this misconception, Table A looks perfect since \(\mathrm{14 \geq 14}\), \(\mathrm{30 \geq 30}\), and \(\mathrm{54 \geq 54}\), leading them to select Choice A (Table A).
The Bottom Line:
This problem tests systematic checking skills more than mathematical calculation. Students must resist the urge to jump to conclusions after checking just one or two pairs from each table.
| x | y |
|---|---|
| 3 | 14 |
| 5 | 30 |
| 7 | 54 |
| x | y |
|---|---|
| 3 | 10 |
| 5 | 34 |
| 7 | 50 |
| x | y |
|---|---|
| 3 | 10 |
| 5 | 26 |
| 7 | 50 |
| x | y |
|---|---|
| 3 | 18 |
| 5 | 34 |
| 7 | 58 |