How to calculate an average
An average is a single value that summarizes a set of numbers. The most common ways to calculate an average are the simple (arithmetic) average, the weighted average (when some values count more than others), and, in the case of school grades, figuring out what score you need to reach a target average.
Simple average formula
average = (sum of all values) ÷ (number of values). The average of 8, 7, and 9 is (8 + 7 + 9) ÷ 3 = 8.
Weighted average formula
weighted average = (value1 × weight1 + value2 × weight2 + ...) ÷ (sum of weights). This is the formula used in most school report cards, where tests and assignments carry different weights. A grade of 8 with weight 2 and a grade of 6 with weight 3 give (8 × 2 + 6 × 3) ÷ 5 = 6.8.
Simple average vs. weighted average
In a simple average, every value counts equally. In a weighted average, values with a higher weight influence the final result more. This shows up in schools (a final exam is worth more than a group project), in financial calculations, and in any situation where not everything carries the same importance.
How to calculate the score you need
To find out what score you need on the remaining evaluations to hit a target average, the formula is: score needed = (target average × total grades − sum of grades already earned) ÷ grades remaining. If the result is higher than the maximum possible score, that average may no longer be reachable with the remaining evaluations.