There were 800 x 20/100 = <<800*20/100=160>>160 parents who agreed to the tuition fee increase.

So, there were 800 - 160 = <<800-160=640>>640 parents who disagreed.

# Answer

640
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
A survey conducted by the school showed that only 20% of the 800 parents agree to a tuition fee increase. How many parents disagree with the tuition fee increase?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
640
A survey conducted by the school showed that only 20% of the 800 parents agree to a tuition fee increase. How many parents disagree with the tuition fee increase?
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