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x = 64y = sqrt[3]{x + 12}The graphs of the given equations intersect at the point \(\mathrm{(x, y)}\) in the...

GMAT Advanced Math : (Adv_Math) Questions

Source: Prism
Advanced Math
Nonlinear equations in 1 variable
EASY
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Notes
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\(\mathrm{x = 64}\)

\(\mathrm{y = \sqrt[3]{x} + 12}\)

The graphs of the given equations intersect at the point \(\mathrm{(x, y)}\) in the xy-plane. What is the value of y?

  1. \(\mathrm{4}\)
  2. \(\mathrm{16}\)
  3. \(\mathrm{20}\)
  4. \(\mathrm{76}\)
A

4

B

16

C

20

D

76

Solution

1. TRANSLATE the intersection condition

  • Given information:
    • \(\mathrm{x = 64}\)
    • \(\mathrm{y = \sqrt[3]{x} + 12}\)
    • These graphs intersect at point \(\mathrm{(x, y)}\)
  • What this tells us: Since the point \(\mathrm{(x, y)}\) lies on both graphs, it must satisfy both equations simultaneously

2. TRANSLATE the solution strategy

  • We know \(\mathrm{x = 64}\), so we can substitute this value into the y equation
  • This will give us the y-coordinate of the intersection point

3. SIMPLIFY through substitution and calculation

  • Substitute \(\mathrm{x = 64}\) into \(\mathrm{y = \sqrt[3]{x} + 12}\):
    \(\mathrm{y = \sqrt[3]{64} + 12}\)
  • Evaluate the cube root:
    \(\mathrm{\sqrt[3]{64} = 4}\) (since \(\mathrm{4^3 = 4 \times 4 \times 4 = 64}\))
  • Complete the addition:
    \(\mathrm{y = 4 + 12 = 16}\)

Answer: B (16)




Why Students Usually Falter on This Problem

Most Common Error Path:

Weak conceptual knowledge about cube roots: Students may confuse cube roots with square roots or not recognize that \(\mathrm{\sqrt[3]{64} = 4}\).

Some students might calculate \(\mathrm{\sqrt{64} = 8}\) instead of \(\mathrm{\sqrt[3]{64} = 4}\), leading to \(\mathrm{y = 8 + 12 = 20}\). This may lead them to select Choice C (20).

Second Most Common Error Path:

Poor TRANSLATE reasoning: Students might not understand what "intersection point" means and attempt to solve both equations as a system rather than recognizing they should substitute the given x-value.

This leads to confusion about the problem setup and may cause them to get stuck and guess randomly.

The Bottom Line:

This problem tests whether students understand intersection points and can work with cube roots. The key insight is recognizing that intersection means substitution, and then accurately evaluating \(\mathrm{\sqrt[3]{64} = 4}\).

Answer Choices Explained
A

4

B

16

C

20

D

76

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