It’s your best friends birthday and you invite him and a group of friends to Chili’s. The restaurant bill was $42 dollars. The waiter treated you really well and you want to give him an extra 10% percent tip. How much money will you pay the waiter??  Answer: To make a quick calculation mentally, all you have to do is move the decimal point one place to the left.  $42. = 4.2 = $4.20 is 10% which is what you should give the waiter.  Rule #1: 10% of a number is 1 of a number. 10  You can solve it mentally by moving the decimal point to the left 1 space. Example: 10% of 270 = or 27.

Rule #2: 1% of a number is 1 of a number. 100 You can solve it mentally by moving the decimal point 2 places to the left. Example: 1% of 270 = or 2.7 Rule #3: 50% of a number is 1 of the number, which means half times the number. 2 Example: 50% of 270 = 135 You can solve it mentally by taking the number and dividing it by 2.

When you are not sure about the percent of a number, all you have to do is write the percent as a decimal and multiply by the number in the problem.  Example: 25% of 500 .25 x 500 = 125 Your Example:  50% of 6=5% of 300 =  20% of 80 =90% of 500 =

Homework: Find 50%, 10% and 1% of each number. (3 checks each) 1. 27, ,  Use mental math to find each percent. (1 check each) 6. 25% of % of % of % of $ % of 80