Quick Percentage Increases

Mental Math · Axiom Academy

LESSON Quick Percentage Increases Master mental math techniques for calculating tax, tips, and markups - find 110%, 115%, or 120% of any number instantly 1. Understanding Percentage Increases When we add a percentage to a number, we're finding more than 100% of the original. For example, adding 15% tax means we need 100% (the original price) plus 15% more, which equals 115% of the original. This means we multiply by a decimal slightly larger than 1 The key to mental math is recognizing that each percentage increase has a simple multiplier. Let's learn the most common ones you'll use in everyday life. Used for: 10% tax, 10% tip, 10% markup Used for: 15% tip (standard service) Used for: 20% tip (excellent service), 20% markup Used for: 25% discount reversal, 25% markup Now let's learn practical techniques to multiply these numbers in your head quickly. Each strategy breaks the calculation into easier mental chunks. Problem: A 40 item with 10% tax. What's the total? 10% of 40 = 4 (move decimal left) Mental shortcut: "40 plus 4 equals 44" Problem: 60 restaurant bill with 15% tip. What's the total? Mental shortcut: "60 plus 6 plus 3 equals 69" Problem: 80 meal with 20% tip. What's the total? Double it: 8 × 2 = 16 (that's 20%) Mental shortcut: "80 plus 16 equals 96" Problem: 32 cost with 25% markup. What's the price? 25% is one-quarter: 32 ÷ 4 = 8 Mental shortcut: "32 plus 8 equals 40" Test your skills! Click "Show Answer" to reveal the solution and the mental math strategy used.

This is the written version of the interactive lesson above. See the full Mental Math course.