Quick brief
What to know before you calculate
A short read on the assumptions, trade-offs and definitions that shape the answer.
- A simple average treats every value equally.
- A weighted average gives larger items more influence.
- Weights must describe the real importance, credits, quantities or sample sizes.
What a simple average assumes
A simple average adds the values and divides by the number of values. It works well when each value should count the same. If one exam is worth 70 percent of a course and another is worth 30 percent, a simple average can misstate the final result.
What a weighted average changes
A weighted average multiplies each value by its weight, adds the weighted values, then divides by the total weight. The weight might be course credits, sales volume, investment size, survey responses or any other measure of importance.
Common real-world examples
Grades often use credits or assessment weights. Product prices can use quantities sold. Portfolio returns can use the amount invested in each holding. Survey results can use sample sizes so a small group does not count the same as a large group.
Check the weights before trusting the answer
Weights should come from the real structure of the problem, not from a convenient guess. If the weights do not represent actual importance, a weighted average can look precise while still being misleading.
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