Percents
What you'll learn
Turn any 'percent of' or 'percent change' question into a calculation you can do.
Percent means "per hundred." 25% is 25 per 100, or 0.25. Once you see that, every percent question becomes a small multiplication.
Percent of a number
"P% of W" is (P ÷ 100) × W. So 20% of 80 is 0.20 × 80 = 16.
Percent change
To compare a before and an after, take the change over the original, times 100:
From 50 to 65: (65 − 50) ÷ 50 × 100 = +30%. A drop would come out negative.
The catch — and the most common percent mistake — is that percent change is always over the original value, never the new one. The pre-algebra solver has a mode for each of these.
Check your understanding
Question 1 of 2
What is 20% of 80?