The formula to find the average of a data is given as follow Mean = The sum of the data value ÷ Number of data
We would need the sum of 32 values to work out the mean score of 32 students. We will work out separately by finding the sum of scores of 12 students and sum of scores of 20 students
90 = Sum of data ÷ 12 Sum of data = 90×12 = 1080 scores
80 = Sum of data ÷ 20 Sum of data = 80×20 = 1600 scores
The sum of data of 32 students is 1080+1600 = 2680 scores Mean = 2680÷32 = 83.75