Official Solution: Machine A, operating at a constant rate, can process a 900-unit order in 36 minutes. How many minutes would it take to process the order if Machine A and Machine B worked together at their respective constant rates? Since the rate of Machine A and the size of the job are known, we only need to determine the rate of Machine B to answer the question. Once both rates are known, we can compute the combined rate and the required time. So we focus only on whether B's rate can be determined and avoid unnecessary calculation.
(1) Machine A processes twice as many units as Machine B in the same amount of time.
This gives a direct relationship between their rates: A's rate = 2 * B's rate. Since A's rate is known, we can determine B's rate. Sufficient.
(2) Machine B takes three times as long to process the entire order alone as it takes both machines working together.
This statement implies 3 * B's rate = A's rate + B's rate. From this, we get A's rate = 2 * B's rate. Since A's rate is known, we can determine B's rate. Sufficient.
Answer: D