01 Key Concepts
Average Formula
Add up all the values, then divide by how many values there are.
Weighted Average
Used when some values count more than others; multiply each value by its weight, sum them, and divide by the total weight.
Finding a Missing Value
If you know the average and all but one value, multiply the average by the count to find the total, then subtract the known values.
Effect of Adding a Value
Adding a new value changes the total count and total sum, which shifts the average up or down.
03 Key Formulas
- Average = Sum of values / Number of values
04 Solved Examples
Example 1 Find the average of 4, 8, 6, and 10.
- Sum = 4+8+6+10 = 28.
- Count = 4 values.
- Average = 28 ÷ 4.
Answer: 7
Example 2 The average of 5 numbers is 20. Four of them are 15, 18, 22, and 25. Find the fifth.
- Total sum = average x count = 20 x 5 = 100.
- Sum of known 4 numbers = 15+18+22+25 = 80.
- Fifth number = 100 - 80.
Answer: 20
Example 3 A student scores 70, 80, and 90 on three tests. What score is needed on a fourth test to average 85?
- Needed total = 85 x 4 = 340.
- Current total = 70+80+90 = 240.
- Needed score = 340 - 240.
Answer: 100
05 Practice Questions
1Find the average of 10, 20, 30.
20
2Find the average of 5, 7, 9, 11.
8
3The average of 3 numbers is 15; two of them are 10 and 12. Find the third.
23
4Find the average of 100, 200, 300, 400.
250
5A car travels at speeds 40, 60, 50 km/h on three legs of equal duration. Find the average speed.
50 km/h
📄 Average — Downloadable Worksheet
10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.