Percents
Per hundred — a fraction wearing a different hat.
Concept
Percent is just /100
25% means 25 per hundred, which is 25/100, which is 0.25. Those three forms are interchangeable.
'Of' means multiply. So 'what is 25% of 80' is 0.25 × 80.
p% of n = (p / 100) × n