Ten-Percent Tricks

Every mental percentage starts from one move: 10% means slide the decimal one place left. On a $64 bill, 10% is $6.40. From there you scale:

• 20% = double it = $12.80
• 5% = half of 10% = $3.20
• 15% = 10% + 5% = $9.60
• 25% = divide by 4 = $16.00

Any rate ending in 5 is just 10% and 5% chunks added together. Try it on a real check this week and compute the tip before your phone unlocks.