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?
There were 800 x 20/100 = 
<gadget id="calculator">800*20/100</gadget>
<output>160</output>
160 parents who agreed to the tuition fee increase.
So, there were 800 - 160 = 
<gadget id="calculator">800-160</gadget>
<output>640</output>
640 parents who disagreed.

<result>640</result>