Math prob in textbook: the price of a liter of coke increased from 1.09 to 1.29. what was the percent of increase? i know how to do it, but i don't understand the answer. i got . on and on. the book said approximately 18.3% how did they get that? where did the decimal come from? how would i round that non ending decimal to a percent money-wise?

You did every bit of the tough part, and did it masterfully.

Now, go back a few months or a year in your memory, to the time when
you learned how to express a number as a percentage.  Do you remember ? 

To change a number to a percentage, either multiply it by 100, or move the
decimal point two places that way ===> .  (The same thing.)

The number you got was correct.  When you increase 1.09 to 1.29, you have
increased the 1.09 by 0.1834862... of it. 

What percent of 1.09 is 0.1834862... of it ?

Change the number 0.1834862... to a percent . . . . . 18.34862... percent.

Usually, nobody cares about all those decimal places, so you usually just
round it to the nearest 0.1 percent, or even the nearest whole percent.

What did the book say ?  Approximately 18.3% ?  OK. Round 18.34862...% to the
nearest 0.1.  That's 18.3% .