* 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 重量 (wi) times the data number (xi) divided by the sum of the weights:
Find the weighted average of class grades (with equal 重量) 70,70,80,80,80,90:
Since the 重量 of all grades are equal, we can 计算 these grades with simple average or we can count how many times each 成绩 appears and use weighted average.
2×70,3×80,1×90
