For the weighted average, here’s the complete manual equation:
wa = (89*10%)+(92*20%)+(95*5%)+(90*15%)+(92*20%)+(91*30%)/10%+20%+5%+15%+20%+30%
Pretty daunting, right?
As mentioned earlier, when computing for the weighted average, you’ll have to multiply the values to their weights and add the products.
Then, instead of dividing the result with the total number of values, you’ll have to divide the product of the first half of the formula with the sum of all the weights.
Now, let’s simplify the weighted average computation by using the ‘SUM’ function in Excel.
Here’s the syntax of ‘SUM’:
=SUM(number 1, [number 2], …)
When applied to the weighted average formula, we’ll then arrive at:
wa =SUM(B3*C3, B4*C4, B5*C5, B6*C6, B7*C7, B8*C8)/SUM(C3:C8)
In the formula above, the SUM function shortened the 2nd half of the formula where the weights are added.
The weighted average is 91.25. That’s a 0.25 difference compared to its normal average.