$14 meal; 20% tip me on this it is mathematics

The tip would be $2.80 because it is 20% of the $14 meal

First, convert the 20% to an actual number that can be used in a calculation. For percents,this is always done by simply dividing the percent (in this case 20%) by 100%.So, the conversational term "20%" becomes 20% / 100% = 0.20 in terms of a real mathematical number.
Second, you need to find out what 20% of your $14 meal cost is.This is always done by multiplying 0.20 by $14.00, or

0.20 x $14.00=$2.80.
So, the amount of tip you are going to leave is $2.80.

This makes the total cost of your meal (to write on your charge slip or other payment)

$14.00 + $2.80 = $16.80.

Quick tip calculation for 15% tips:

If you're leaving the standard 15% tip, here's a quick and easy way to calculate it in your head, at the table in the restaurant, without embarassing yourself by scribbling all over the back of a receipt or getting out a calculator:
15% is 10% + 5% (or 0.15 = 0.1 + 0.05, dividing each percent by 100). Thinking about it this way is useful for two reasons. First, it's easy to multiply any number by 0.1; just move the decimal point left one digit. For example, 75.00 x 0.1 = 7.50, or 346.43 x 0.1 = 34.64 (close enough). Second, 5% is exactly half of 10%. So here's how this quick and easy method works:
Take the total cost of your meal, $14.00 and multiply it by 0.1 by sliding the decimal to the left one digit to get $1.40 (you can do this in your head at the table). $1.40 is 10% of your meal cost. But the proper tip to leave is 15% (you need to throw in another 5%).

The additional 5% is just half of the 10% amount. What is half of $1.40? About $0.70. (Finding half of a number is also something you can do in your head at the table.) So, the total tip to leave is the 10% amount PLUS the 5% amount (for a 15% tip) or $1.40 + $0.70 = $2.10 .

The general rule here is:

Find the number that results from sliding the decimal point of the meal's cost left one digit,
and add on another half of this number.

That's your tip!