Alright, let's break this problem apart, shall we?
685 sixth grade students is 100%.
What do we need to do? We need to find 80% of 100% (685 students).
80% is 0.8 of 1.0.
1.0 is 685 students.
We need to multiply 685 students by 0.8.
685 * 0.8 = 548 students.
548 students are going are going to the field-trip.
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