* SD = standard deviation
The average (arithmetic mean) is equal to the sum of the n numbers divided by n:
The average of 1,2,5 is:
The weighted average (x) is equal to the sum of the product of the weight (wi) times the data number (xi) divided by the sum of the weights:
Find the weighted average of class grades (with equal weight) 70,70,80,80,80,90:
Since the weight of all grades are equal, we can calculate these grades with simple average or we can count how many times each grade appears and use weighted average.