Question: Utopia National Park hosted 30,000 elephants on Friday night. The next morning, there was a 4-hour elephant exodus out of the park, at a constant rate of 2,880 elephants/hour. Over the next 7-hour period, new elephants entered the park at a constant rate. If the final number of elephants in the park was 28,980, at what rate did the new elephants enter the park? Think carefully first, then make a decision:
The Saturday morning exodus out of the park comprised 4 * 2880 = 11520 elephants. This means that after the exodus, the park was left with 30000 - 11520 = 18480 elephants. Since the final number of elephants was 28,980, the new elephants that entered were 28980 - 18480 = 10500. The rate at which the new elephants entered the park was therefore 10500 / 7 = 1500 elephants / hour. So the answer is 1500.