The perimeter of the lake is 4*15=<<4*15=60>>60 miles

He swims at a speed of 60/20=<<60/20=3>>3 mph

So he rows at a speed of 3*2=<<3*2=6>>6 mph

That means it takes him 60/6=<<60/6=10>>10 hours to row around the lake

# Answer

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<|im_start|>system
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<|im_start|>user
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?
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<|im_start|>assistant

user
10
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?
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