The price of a notebook was $3.30 yesterday. today, the price rose to $3.80 . find the percentage increase.

.50 / 3.30 * 100 = 15.15%

First you find the difference between the two prices:
3.80-3.30 = 0.50

Then you divide the Difference by the original price and times it by 100 to get the percentage increase:
0.50/3.30 = 0.1515
0.1515 * 100 = 15.15%

Hello this helps! :)