Mark played for a total of 20 + 35 = <<20+35=55>>55 minutes.

So, he was on the sideline for 90 - 55 = <<90-55=35>>35 minutes.

# Answer

35
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
In a 90-minute soccer game, Mark played 20 minutes, then rested after. He then played for another 35 minutes. How long was he on the sideline?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
35
In a 90-minute soccer game, Mark played 20 minutes, then rested after. He then played for another 35 minutes. How long was he on the sideline?
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