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A lab notebook has room for 24 data entries on the first page because of a title block. Each additional...

GMAT Algebra : (Alg) Questions

Source: Prism
Algebra
Linear functions
HARD
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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 \(\mathrm{x \leq 15}\)?

A

\(\mathrm{y = 24x}\)

B

\(\mathrm{y = 28x}\)

C

\(\mathrm{y = 28x + 24}\)

D

\(\mathrm{y = 28x - 4}\)

Solution

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.

Answer Choices Explained
A

\(\mathrm{y = 24x}\)

B

\(\mathrm{y = 28x}\)

C

\(\mathrm{y = 28x + 24}\)

D

\(\mathrm{y = 28x - 4}\)

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