What is the new class average?

Question

The average mark in a FOM 11 class is 73%. There were 15 students in the class. Josh and Amy were missing when the test was written and wrote it a day later. Their marks were 89% and 95%. What is the new class average?

Answer 1

Let s = sum of the grades of the 15 students

 

s/15 = 73

s = 73(15)

s = 1095

 

The new sum is (s + 89 + 95) = 1095 + 184 = 1279

The new number of data points is 17

 

1279/17 = 75.23% ... 

 

If rounding to nearest whole number average the answer is 75%