Given the stream of consciousness rationale, provide a reasonable question and answer. Rationale: Nathan can do 20 x 2 = 40 sit ups. Ken and Nathan's combined number is 20 + 40 = 60 sit - ups. Bob can do 60 / 2 = 30 sit - ups. Bob can do 30 - 20 = 10 more sit - ups than Ken.
 The question and answer:
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?
The answer is 10