Let's say your bill at a restaurant comes to $60.00 and you want to give a 15% tip. Now, we know that 10% of 60 is 6, because you move the decimal over one spot. To get to 15%, we need to add 5% more, which is half of 10%. Since 10% is 6, 5% is 3. All we have to do is add 3 and 6 together.
3+6=9
So, 15% of 60 is 9,which means you would tip $9!