7 Percentage Tricks for Mental Math
Calculate tips, discounts, and raises in your head with these seven tricks.
1. The 10% Anchor: move the decimal left. 10% of $67.50 = $6.75. Build from there: 20% = double it, 5% = half of 10%, 15% = 10% + 5%. 2. The Flip Trick: 8% of 50 = 50% of 8 = 4. Pick whichever is easier. 3. Discounts: subtract from 100. 30% off means you pay 70%. $80 at 30% off: 70% of $80 = $56.
Advanced Tricks
4. Double discounts are not additive: 40% off plus 20% off is NOT 60% off. It is 0.6 times 0.8 = 52% off. 5. The Rule of 72: years to double money = 72 / return rate. At 8%: 9 years. At 12%: 6 years. 6. Tip shortcut: double the tax amount for approximately 15-20%. 7. Quick salary to hourly: divide annual by 2,000. $50,000 / 2,000 = $25/hour.