You start with 4 green and 2 red. When Bethany removes a green, you now have 3 green and 2 red apples. You then add to get the total number of apples(3+2=5), and make a fraction by using the total number of apples as the denominator, and the number of red apples as the numerator; 2/5, which if converted to a percentage = 40%(2/5 = 0.4, 0.4 x 100 = 40).