What does it mean to find 15% of 80 and how do I calculate it?

Percent means 'out of 100', so 15% is the same as the fraction 15/100 or the decimal 0.15. The word 'of' in maths means multiply. So 15% of 80 = (15/100) × 80. You can simplify before multiplying: 80 ÷ 100 = 0.8, then 15 × 0.8 = 12. Or do it as a fraction: (15 × 80)/100 = 1200/100 = 12. Either way the answer is 12. A quick mental trick: 10% of 80 is 8, and 5% is half of that, which is 4, so 15% is 8 + 4 = 12. Practising the 10% shortcut makes percentage sums much faster in exams.