Question. John decided to start rowing around a square lake. Each side of the lake is 15 miles. Jake can row at twice the speed he can swim. It takes him 20 minutes to swim 1 mile. How long, in hours, does it take to row the lake?
Answer. 10
What step-by-step reasoning justifies that answer?
Reasoning: The perimeter of the lake is 4 * 15 = 60 miles. He swims at a speed of 60 / 20 = 3 mph. So he rows at a speed of 3 * 2 = 6 mph. That means it takes him 60 / 6 = 10 hours to row around the lake.