The functions h and k are defined by the given equations.\(\mathrm{h(x) = 1 + |x^2 - 5x|}\)\(\mathrm{k(t) = |\frac{6}{t-1}| -...
GMAT Advanced Math : (Adv_Math) Questions
The functions h and k are defined by the given equations.
\(\mathrm{h(x) = 1 + |x^2 - 5x|}\)
\(\mathrm{k(t) = |\frac{6}{t-1}| - t + 8}\), where \(\mathrm{t \neq 1}\)
If \(\mathrm{h(6) = d}\), where d is a constant, what is the value of \(\mathrm{k(d)}\)?
1. TRANSLATE the problem information
- Given information:
- \(\mathrm{h(x) = 1 + |x² - 5x|}\)
- \(\mathrm{k(t) = |6/(t-1)| - t + 8}\), where \(\mathrm{t ≠ 1}\)
- \(\mathrm{h(6) = d}\) (we need to find d first)
- Find \(\mathrm{k(d)}\)
- What this tells us: We have a two-step process - first evaluate h at x = 6, then use that result as input for function k.
2. SIMPLIFY to find h(6)
- Substitute x = 6 into h(x):
\(\mathrm{h(6) = 1 + |6² - 5(6)|}\)
- Calculate inside the absolute value first:
\(\mathrm{6² - 5(6) = 36 - 30 = 6}\)
- Apply absolute value: \(\mathrm{|6| = 6}\)
- Complete the calculation: \(\mathrm{h(6) = 1 + 6 = 7}\)
- Therefore: \(\mathrm{d = 7}\)
3. SIMPLIFY to find k(7)
- Substitute t = 7 into k(t):
\(\mathrm{k(7) = |6/(7-1)| - 7 + 8}\)
- Calculate the fraction: \(\mathrm{6/(7-1) = 6/6 = 1}\)
- Apply absolute value: \(\mathrm{|1| = 1}\)
- Complete the calculation: \(\mathrm{k(7) = 1 - 7 + 8 = 2}\)
Answer: 2
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak SIMPLIFY execution: Students make arithmetic errors when evaluating \(\mathrm{6² - 5(6)}\), calculating it as \(\mathrm{6² - 5 × 6 = 36 - 5 × 6 = 36 - 11 = 25}\) instead of \(\mathrm{36 - 30 = 6}\).
This leads to \(\mathrm{h(6) = 1 + |25| = 26}\), so \(\mathrm{d = 26}\), then \(\mathrm{k(26)}\) requires evaluating k at an unintended value, causing confusion and likely guessing.
Second Most Common Error:
Poor TRANSLATE reasoning: Students misunderstand the two-step nature of the problem, trying to find \(\mathrm{k(6)}\) directly instead of first finding \(\mathrm{d = h(6)}\), then evaluating \(\mathrm{k(d)}\).
This causes them to substitute 6 into the k function immediately, getting \(\mathrm{k(6) = |6/(6-1)| - 6 + 8 = |6/5| - 6 + 8 = 1.2 + 2 = 3.2}\), leading to confusion since this doesn't match typical answer formats.
The Bottom Line:
This problem tests your ability to follow a multi-step process systematically while handling absolute values correctly. The key is recognizing that you must complete the first function evaluation entirely before moving to the second function.