The equation (15p - 5q)/5 = 3sqrt(t) + 1 relates the distinct positive real numbers p, q, and t. Which...
GMAT Advanced Math : (Adv_Math) Questions
The equation \(\frac{15\mathrm{p} - 5\mathrm{q}}{5} = 3\sqrt{\mathrm{t}} + 1\) relates the distinct positive real numbers p, q, and t. Which of the following expresses t in terms of p and q?
1. SIMPLIFY the left side of the equation
- Given: \(\frac{15p - 5q}{5} = 3\sqrt{t} + 1\)
- Distribute the division: \(\frac{15p - 5q}{5} = \frac{15p}{5} - \frac{5q}{5} = 3p - q\)
- The equation becomes: \(3p - q = 3\sqrt{t} + 1\)
2. INFER the strategy to isolate the radical term
- Goal: Get \(\sqrt{t}\) by itself so we can square both sides
- First step: Move the constant term to isolate \(3\sqrt{t}\)
3. SIMPLIFY by moving the constant term
- Subtract 1 from both sides: \(3p - q - 1 = 3\sqrt{t}\)
- Now we have the radical term isolated on one side
4. SIMPLIFY to get √t alone
- Divide both sides by 3: \(\frac{3p - q - 1}{3} = \sqrt{t}\)
- Now \(\sqrt{t}\) is completely isolated
5. SIMPLIFY by eliminating the square root
- Square both sides: \(t = \left[\frac{3p - q - 1}{3}\right]^2\)
- This matches answer choice (B)
Answer: B
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak SIMPLIFY execution: Students make arithmetic errors when simplifying \(\frac{15p - 5q}{5}\), often getting \(3p - q\) + something wrong or forgetting to distribute the division properly.
For example, they might write \(\frac{15p - 5q}{5} = 15p - q\) or \(3p - 5q\), leading to completely incorrect subsequent steps. This leads to confusion and guessing since none of their algebra will match the answer choices.
Second Most Common Error:
Poor INFER reasoning about equation solving strategy: Students attempt to square both sides too early, before properly isolating the radical term.
They might try to square \(3p - q = 3\sqrt{t} + 1\) immediately, creating a complex expression \((3\sqrt{t} + 1)^2 = 9t + 6\sqrt{t} + 1\) that's much harder to work with. This may lead them to select Choice A \((3p - q - 1)^2\) because they see a similar structure but haven't properly isolated the variable.
The Bottom Line:
This problem tests systematic algebraic manipulation skills. Success requires methodically isolating the radical term before attempting to eliminate it, combined with careful arithmetic throughout multiple steps.