\(\mathrm{y For which of the following tables are all the values of x and their corresponding values of y solutions...
GMAT Algebra : (Alg) Questions
\(\mathrm{y < 6x + 2}\)
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 |
|---|---|
| 3 | 20 |
| 5 | 32 |
| 7 | 44 |
| x | y |
|---|---|
| 3 | 16 |
| 5 | 36 |
| 7 | 40 |
| x | y |
|---|---|
| 3 | 16 |
| 5 | 28 |
| 7 | 40 |
| x | y |
|---|---|
| 3 | 24 |
| 5 | 36 |
| 7 | 48 |
1. TRANSLATE the inequality requirement
- Given: \(\mathrm{y < 6x + 2}\)
- We need ALL values in a table to satisfy this inequality
- This means for each x-value, the corresponding y-value must be less than \(\mathrm{6x + 2}\)
2. INFER the systematic approach
- Since all tables use the same x-values (3, 5, 7), calculate the boundary for each:
- For each x, find what \(\mathrm{6x + 2}\) equals, then check if the table's y is less than that value
3. SIMPLIFY to find the boundaries
- For \(\mathrm{x = 3}\): \(\mathrm{6(3) + 2 = 18 + 2 = 20}\), so \(\mathrm{y < 20}\)
- For \(\mathrm{x = 5}\): \(\mathrm{6(5) + 2 = 30 + 2 = 32}\), so \(\mathrm{y < 32}\)
- For \(\mathrm{x = 7}\): \(\mathrm{6(7) + 2 = 42 + 2 = 44}\), so \(\mathrm{y < 44}\)
4. APPLY CONSTRAINTS to each table
Check each table systematically:
Choice A: All y-values equal the boundaries (20, 32, 44) - not less than, so fails
Choice B: \(\mathrm{y = 36}\) when \(\mathrm{x = 5}\), but \(\mathrm{36 > 32}\), so fails
Choice C: All y-values (16, 28, 40) are less than their boundaries (20, 32, 44) ✓
Choice D: All y-values exceed their boundaries, so fails
Answer: C
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE reasoning: Students misinterpret '\(\mathrm{y < 6x + 2}\)' as '\(\mathrm{y \leq 6x + 2}\)' or don't understand that the inequality must be strict.
They see that Choice A has y-values of exactly 20, 32, and 44, which equal \(\mathrm{6x + 2}\) for each corresponding x, and incorrectly think this satisfies the inequality. Since these values equal (rather than are less than) the expression, Choice A fails the strict inequality test.
This may lead them to select Choice A (with y-values 20, 32, 44).
Second Most Common Error:
Poor SIMPLIFY execution: Students make arithmetic errors when calculating \(\mathrm{6x + 2}\), getting wrong boundary values.
For example, calculating \(\mathrm{6(5) + 2}\) as 28 instead of 32, or \(\mathrm{6(7) + 2}\) as 40 instead of 44. With wrong boundaries, they can't properly evaluate which tables satisfy the inequality.
This leads to confusion and guessing among the remaining choices.
The Bottom Line:
This problem tests whether students truly understand strict inequality notation and can systematically check multiple conditions. The key insight is that 'less than' means the y-value cannot equal the boundary - it must be strictly smaller.
| x | y |
|---|---|
| 3 | 20 |
| 5 | 32 |
| 7 | 44 |
| x | y |
|---|---|
| 3 | 16 |
| 5 | 36 |
| 7 | 40 |
| x | y |
|---|---|
| 3 | 16 |
| 5 | 28 |
| 7 | 40 |
| x | y |
|---|---|
| 3 | 24 |
| 5 | 36 |
| 7 | 48 |