Weighted final grade with SUMPRODUCT
Your course grade is not a plain average — the final exam counts for more than the homework. The grading sheet in A2:C5 lists each component's score and its weight (weights sum to 1). Compute the final grade in the Final grade cell E2 by pairing each score with its weight in one formula.
Use one formula that multiplies each score by its weight and adds the results — don't compute each product in a helper cell.
Notes
SUMPRODUCT(array1, array2) multiplies the pairs row by row and adds everything up in one step: score × weight for every row, then the total. When the weights sum to 1 the result is the weighted average. A plain AVERAGE would pretend the 10% project counts as much as the 40% final — a classic interview trap.
Function guide
FAQ
How do I calculate a weighted average in Excel?
Use =SUMPRODUCT(scores, weights) when the weights add up to 1. For example =SUMPRODUCT(B2:B5, C2:C5) multiplies each score by its weight and sums the results in one step.
Why not just use AVERAGE?
AVERAGE treats every component equally. If the final exam is worth 40% and homework 20%, the plain average hides that difference and reports the wrong grade. Weighted averages pair each value with its importance.
What if my weights don't add up to 1?
Divide by their sum: =SUMPRODUCT(B2:B5, C2:C5) / SUM(C2:C5). This normalizes the weights, so the formula keeps working whether they total 100%, 110%, or points.
Does SUMPRODUCT work in Google Sheets?
Yes — SUMPRODUCT behaves identically in Excel and Google Sheets, which is why it's the standard answer for weighted-average interview questions on both platforms.