Nathan can do 20 x 2 = <<20*2=40>>40 sit ups.

Ken and Nathan's combined number is 20 + 40 = <<20+40=60>>60 sit-ups.

Bob can do 60/2 = <<60/2=30>>30 sit-ups.

Bob can do 30 - 20 = <<30-20=10>>10 more sit-ups than Ken.

# Answer

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You are a helpful assistant.<|im_end|>
<|im_start|>user
Ken can do 20 sit-ups without stopping. Nathan can do twice as many, and Bob can do half the number of Ken and Nathan's combined sit-ups. How many more sit-ups can Bob do compared to Ken?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
10
Ken can do 20 sit-ups without stopping. Nathan can do twice as many, and Bob can do half the number of Ken and Nathan's combined sit-ups. How many more sit-ups can Bob do compared to Ken?
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