Correct. 25 is the correct number of cups of peanut butter required to make 100 servings of ice cream. Since 20 servings require 5 cups of peanut butter, 1 serving requires $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ cup of peanut butter, so 100 servings require $\displaystyle{100}\cdot\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ , which equals 25 cups of peanut butter.