There are two groups of students in the sixth grade. There are 20 students in group A, and 80 students in group B. If, on a particular day, 20% of the students in group A forget their homework, and 15% of the students in group B forget their homework, then what percentage of the sixth graders forgot their homework?  Choose the correct choice from the following options
A) 13 %  B) 14 %  C) 15 %  D) 16 %  E) 17 %

Rationale: "number of students in group a = 20 students who forget homework in group a = 20 % of 20 = 4 students number of students in group b = 80 students who forget homework in group b = 15 % of 80 = 12 students total number of students = 20 + 80 = 100 students who forgot homework = 4 + 12 = 16 students percentage of students who forget homework = 16 / 100 * 100 = 16 % answer : d"
Answer: D