Line Plots & Mean • Topic 1 of 2

Finding Mean (Average)

What is Mean (Average)?

The mean is the fair share — if you add all numbers and split equally among all items.

Formula:

Mean = Sum of all values ÷ Number of values

Steps:

  1. Add up all numbers (find the sum)
  2. Count how many numbers (n)
  3. Divide sum by count

Example: Find mean of 5, 7, 12, 8

  • Sum = 5 + 7 + 12 + 8 = 32
  • Count = 4 numbers
  • Mean = 32 ÷ 4 = 8
MEAN AS "FAIR SHARE":

    Data: 4, 6, 8, 10
    
    Step 1: Stack all values:
        │
        │   ■ (10)
        │   ■ (8)
        │   ■ (6)
        │   ■ (4)
        └─────
    
    Step 2: Level them out (each gets same):
        │ ■ ■ ■ ■
        │ ■ ■ ■ ■
        │ ■ ■ ■ ■
        │ ■ ■ ■ ■
        └─────
    
    Each column has 7 → Mean = 7


MEAN ON A NUMBER LINE:

    Data: 2, 4, 9
    
    Sum = 15
    Count = 3
    Mean = 15 ÷ 3 = 5
    
    <---|---|---|---|---|---|---|---|---|--->
        2       4       5       9
                       ↑
                      Mean
    Values balance around 5: (5-2)=3, (5-4)=1, (9-5)=4; 3+1=4 ✓
Solved Examples
1
Worked Example

Find the mean of 12, 15, 18, 20, 25

Solution
  • Sum = 12 + 15 + 18 + 20 + 25 = 90
  • Count = 5
  • Mean = 90 ÷ 5 = 18
  • Answer: 18
2
Worked Example

Maria's test scores: 85, 92, 78, 95, 90. What is her average?

Solution
  • Sum = 85 + 92 + 78 + 95 + 90 = 440
  • Count = 5
  • Mean = 440 ÷ 5 = 88
  • Answer: 88
3
Worked Example

The mean of 4 numbers is 15. Three numbers are 10, 18, and 14. Find the fourth.

Solution
  • Sum of all 4 = mean × count = 15 × 4 = 60
  • Sum of known = 10 + 18 + 14 = 42
  • Fourth = 60 - 42 = 18
  • Answer: 18

Key Points

  • Mean = total ÷ number of items
  • Also called "average"
  • Can be a decimal (not necessarily a data value)
  • Use to find missing number: total - known sum
Quick Check — 4 MCQs
Tap an option to check your answer0 / 4
Q1.The mean (average) equals:
Explanation: Sum over count.
Q2.The mean of $2, 4, 6$ is:
Explanation: $12/3=4$.
Q3.To find the mean, first you:
Explanation: Add them all.
Q4.The mean of $5, 5, 5$ is:
Explanation: $5$.
Practice more MCQs → 📝 Assignment · 35 marks