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For the linear function g, the graph of \(\mathrm{y = g(x)}\) in the xy-plane has a slope of 2 and...

GMAT Algebra : (Alg) Questions

Source: Practice Test
Algebra
Linear functions
MEDIUM
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Notes
Post a Query

For the linear function g, the graph of \(\mathrm{y = g(x)}\) in the xy-plane has a slope of 2 and passes through the point \(\mathrm{(1, 14)}\). Which equation defines g?

A

\(\mathrm{g(x) = 2x}\)

B

\(\mathrm{g(x) = 2x + 2}\)

C

\(\mathrm{g(x) = 2x + 12}\)

D

\(\mathrm{g(x) = 2x + 14}\)

Solution

1. TRANSLATE the problem information

  • Given information:
    • Slope = 2
    • Graph passes through point (1, 14)
    • Need to find equation g(x)

2. INFER the approach

  • Since this is a linear function with known slope, use slope-intercept form
  • Set up: \(\mathrm{g(x) = mx + b}\) where \(\mathrm{m = 2}\)
  • This gives us: \(\mathrm{g(x) = 2x + b}\)
  • Now need to find the y-intercept b using the given point

3. TRANSLATE the point condition into an equation

  • "Passes through (1, 14)" means when \(\mathrm{x = 1, g(x) = 14}\)
  • Substitute into our equation: \(\mathrm{14 = 2(1) + b}\)

4. SIMPLIFY to find b

  • \(\mathrm{14 = 2(1) + b}\)
  • \(\mathrm{14 = 2 + b}\)
  • \(\mathrm{b = 14 - 2 = 12}\)

5. Write the final equation

  • \(\mathrm{g(x) = 2x + 12}\)

Answer: C. g(x) = 2x + 12




Why Students Usually Falter on This Problem

Most Common Error Path:

Weak INFER skills: Students see the point (1, 14) and think the y-intercept b must equal 14, without recognizing they need to substitute the point into the equation to solve for b.

They incorrectly reason: "The function passes through (1, 14), so the equation must have 14 in it somewhere." This leads them to select Choice D (g(x) = 2x + 14).

Second Most Common Error:

Poor SIMPLIFY execution: Students correctly set up \(\mathrm{14 = 2 + b}\) but make arithmetic errors, such as adding instead of subtracting: \(\mathrm{b = 14 + 2 = 16}\).

Since 16 isn't among the y-intercept values in the choices, this leads to confusion and guessing.

The Bottom Line:

This problem tests whether students understand that "passing through a point" creates a constraint equation that must be solved, rather than directly incorporating the point's coordinates into the final answer.

Answer Choices Explained
A

\(\mathrm{g(x) = 2x}\)

B

\(\mathrm{g(x) = 2x + 2}\)

C

\(\mathrm{g(x) = 2x + 12}\)

D

\(\mathrm{g(x) = 2x + 14}\)

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