Bunuel
Thor, drinking at a constant rate, can finish k liters of beer in m minutes, while Loki, drinking at a slower constant rate, can finish the same k liters in n minutes. If they start drinking together and consume 2k liters in total, in terms of m, n, and k, how much more beer in liters did Thor drink than Loki?
A. \(\frac{k(m - n)}{2(m+n)}\)
B. \(\frac{k(m - n)}{m+n}\)
C. \(\frac{2k(n - m)}{m+n}\)
D. \(\frac{2k(m - n)}{m+n}\)
E. \(\frac{2k(m + n)}{n-m}\)
GMAT Club Official Explanation:
Thor can drink k liters in m minutes: \(rate_{Thor} = \frac{\text{amount}}{\text{time}} = \frac{k}{m}\) liters per minute.
Loki can drink k liters in n minutes: \(rate_{Loki} = \frac{\text{amount}}{\text{time}} = \frac{k}{n}\) liters per minute.
Together, to consume 2k liters at the combined rate of \(\frac{k}{m} + \frac{k}{n}\) liters per minute, they'd take:
\(time = \frac{\text{amount}}{\text{combined rate}} = \frac{2k}{\frac{k}{m} + \frac{k}{n}} = \frac{2k}{k(\frac{1}{m} + \frac{1}{n})} = \frac{2}{\frac{1}{m} + \frac{1}{n}} = \frac{2mn}{m + n}\) minutes.
Therefore, the difference in amounts consumed would be:
{Time} * {Rate of Thor} − {Time} * {Rate of Loki} =
\(= \frac{2mn}{m + n} * \frac{k}{m} - \frac{2mn}{m + n} * \frac{k}{n} = \frac{2k(n - m)}{m + n}\) liters.
Answer: C.