The grade point average of one third of the classroom is 15; the grade point average of the rest is 18. What is the grade point average of the whole class? Choose the correct choice from the following options.
A) 17
B) 19
C) 21
D) 23
E) 25

Rationale: "let n = total students in class total points for 1 / 3 class = 15 n / 3 = 5 n total points for 2 / 3 class = 18 * 2 n / 3 = 12 n total points for whole class = 5 n + 12 n = 17 n 17 n total class points / n total students = 17 grade point average for total class answer : a"
Answer: A