Question

There are 30 students in a class that took a test. The average grade of 10 students was 80. The other 20 students average was 89. What is the overall average for all 30 students?

Answer 1

10 students averaged 80, so the sum of their scores was (10 x 80) = 800

20 students averaged 89, so the sum of their scores was (20 x 89) = 1,780

All together, the sum of all 30 scores was (800 + 1,780) = 2,580

30 students totaled 2,580, so their average was  (2,580 / 30)  =  86 .