Let us consider last year's price, $2, as the original price of a pineapple. This year, the price has risen to $4. So the increase in pineapple price is 4 - 2 = $2. To convert the price increase into a percent, follow this step: Increase in price/original cost x 100. That is, 2/2 x 100 = 100. Thus, there has been a 100 percent rise in the price of pineapple over a one year period.