So you are going to pay $20 and then a 15% tip on top of the 20.
And the 15% tip is 15% of $20.
To do less work, you can basically do 115% of 20 to find out the total cost instead of doing 15% of 20 and then adding that to 20.
Saying that x is the final price to pay, and converting the percents to fractions we get:
\(\sf{\frac{115}{100}\times 20=x}\)
Simplify that:
\(\sf{\frac{115}{5} = x}\)
And simplifying that further, you get the final answer as:
\(\huge{\boxed{\bf{x=23}}}\)
So you have to pay $23 after the tip :)
