You can find 10% of your bill by moving the decimal one place to the left. If 26.50 is 100% then 10% is 2.65. Since 20% is 2 times 10%, 20% of the bill is 2.65 + 2.65 = 5.30. Now you know the tip you could leave ranging from poor to good, $2.65 to $5.30. To find 15%, halfway in between, we know 15% is 10% plus 1/2 of 10% (5%). 2.65 plus about 1.30 is 3.95.
