Percentages: Increase, Decrease, and Applications

A percentage is a fraction out of 100: [formula] Three types of problems: 1. What is p% of N? → frac{p}{100} times N 2. A is what percent of B? → frac{A}{B} times 100 3. A is p% of what? → frac{A}{p/100} = frac{100A}{p}

Example: What is 15% of 240?

Percent change formula: [formula] Shortcut multipliers: - Increase by p%: multiply by (1 + frac{p}{100}) - Decrease by p%: multiply by (1 - frac{p}{100}) Example: A 200 item after a 25% discount: 200 times 0.75 = 150

Example: A stock price goes from 80 to 92. What is the percent increase?