Mental Math Hacks
Reversible Percentages
Percentages are reversible! Need to figure out 8% of 50? Just flip it. 50% of 8 is 4. Both give you the exact same answer, but one is much easier to do in your head.
The Rule of 72
Want to know how fast something will double? Divide 72 by the growth rate. If inflation is 6%, prices will double in 12 years (72 ÷ 6 = 12).
The 20% Tip Trick
To instantly calculate a 20% tip at a restaurant, simply move the decimal point one place to the left (to find 10%), and then double that number.