Mean, Median, Mode, and Data Analysis

Mean (Average)

$\text{Mean} = \frac{\text{Sum}}{\text{Count}}$

Reverse: Sum = Mean × Count. Useful for finding a missing value.

If 4 tests average 85 and you want a 90 average over 5 tests: Total needed = $90 \times 5 = 450$. Current total = $85 \times 4 = 340$. Need: $450 - 340 = 110$.

Median

Middle value when data is ordered. For even counts, average the two middle values.

Mode

Most frequent value.

Range

Max − Min.

Weighted Average

$\text{Weighted mean} = \frac{\sum (\text{value} \times \text{weight})}{\sum \text{weights}}$

• Reading tables/graphs carefully is as important as calculating.
• Estimated mean from grouped data: use midpoints.