Everyday Math: Tips, Tricks, and Shortcuts

Mental Math for the Real World

You don't always need a calculator. Here are a few shortcuts for everyday math.

1. The 20% Tip Trick

To easily calculate a 20% tip at a restaurant, move the decimal point one place to the left (which gives you 10%), and then double that number.

2. Calculating Sale Discounts

If an item is 30% off, you are paying 70% of the price. Multiply the price by 0.7 to instantly get the final cost.

3. The Rule of 72

To find out how many years it will take an investment to double, divide 72 by your annual interest rate.