In a class of 25 students, the average score on a math test was 78. If 5 new students joined the class and their average score was 90, what is the new average score of all 30 students?

✓ Correct Answer: Option B

Total score for the initial 25 students = 25 * 78 = 1950. Total score for the 5 new students = 5 * 90 = 450. Total score for all 30 students = 1950 + 450 = 2400. New average score = 2400 / 30 = 80.