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
\(\mathrm{x = 64}\)
\(\mathrm{y = \sqrt[3]{x} + 12}\)
The graphs of the given equations intersect at the point \(\mathrm{(x, y)}\) in the xy-plane. What is the value of y?
- \(\mathrm{4}\)
- \(\mathrm{16}\)
- \(\mathrm{20}\)
- \(\mathrm{76}\)
4
16
20
76
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 \(\mathrm{\sqrt[3]{64} = 4}\).
4
16
20
76