A lab notebook has room for 24 data entries on the first page because of a title block. Each additional...
GMAT Algebra : (Alg) Questions
A lab notebook has room for \(\mathrm{24}\) data entries on the first page because of a title block. Each additional page can hold \(\mathrm{28}\) entries. Which equation gives the total number \(\mathrm{y}\) of data entries that can be recorded using \(\mathrm{x}\) pages, where \(\mathrm{x}\) is a positive integer and \(\mathrm{x \leq 15}\)?
\(\mathrm{y = 24x}\)
\(\mathrm{y = 28x}\)
\(\mathrm{y = 28x + 24}\)
\(\mathrm{y = 28x - 4}\)
1. TRANSLATE the problem information
- Given information:
- First page: 24 entries (due to title block)
- Each additional page: 28 entries
- Total pages used: x
- Need equation for total entries y
2. INFER the mathematical structure
- Key insight: The first page is different from all other pages
- For x total pages, we have:
- 1 first page with 24 entries
- (x-1) additional pages with 28 entries each
- Total entries = entries on first page + entries on additional pages
3. TRANSLATE this structure into an equation
- \(\mathrm{y = 24 + 28(x - 1)}\)
4. SIMPLIFY the equation algebraically
- \(\mathrm{y = 24 + 28(x - 1)}\)
- \(\mathrm{y = 24 + 28x - 28}\)
- \(\mathrm{y = 28x - 4}\)
5. Verify with test values
- Test \(\mathrm{x = 1}\): \(\mathrm{y = 28(1) - 4 = 24}\) ✓ (only first page)
- Test \(\mathrm{x = 2}\): \(\mathrm{y = 28(2) - 4 = 52}\) ✓ (first page + one additional: \(\mathrm{24 + 28 = 52}\))
Answer: D
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE skill: Students misinterpret "additional pages" and think all x pages hold 28 entries, leading to \(\mathrm{y = 28x}\).
This may lead them to select Choice B (\(\mathrm{y = 28x}\)).
Second Most Common Error:
Poor INFER reasoning: Students recognize the first page is special but incorrectly think the total should be \(\mathrm{28x + 24}\) (adding the extra capacity rather than accounting for the reduced first page capacity).
This may lead them to select Choice C (\(\mathrm{y = 28x + 24}\)).
The Bottom Line:
This problem tests whether students can handle situations where the first term in a pattern is different from the rest—a common real-world scenario that requires careful setup of the mathematical model.
\(\mathrm{y = 24x}\)
\(\mathrm{y = 28x}\)
\(\mathrm{y = 28x + 24}\)
\(\mathrm{y = 28x - 4}\)