<human>:  Mary's sheep can run 12 feet per second, and her sheepdog can run 20 feet per second. A sheep standing 160 feet away from the sheep dog bolts, and the dog runs after it. How many seconds does it take the dog to catch the sheep?
<bot>: How fast is the dog? ** First find how much faster the dog is than the sheep: 20 feet/second - 12 feet/second = <<20-12=8>>8 feet/second
How many seconds does it take the dog to catch the sheep? ** Then divide the distance the dog needs to run by the speed difference: 160 feet / 8 feet/second = <<160/8=20>>20 seconds
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