Mean from Frequency Tables
Calculating the mean from a frequency table requires a slightly different approach, but you've got this! Instead of adding individual numbers, you multiply each value by its frequency, add all these products together, then divide by the total frequency.
For a simple frequency table, like ages 10, 15, 20, 25, 30 with frequencies 7, 2, 9, 5, 8, you'd calculate: (10×7 + 15×2 + 20×9 + 25×5 + 30×8) ÷ (7+2+9+5+8) = 645 ÷ 31 = 20.81.
Grouped frequency tables with intervals need an extra step - you must find the mid-interval value (m.i.v.) first. For the interval 0-10, the mid-point is 5; for 10-20, it's 15, and so on. Then use these mid-points in your calculation just like regular values.
Pro Tip: Always double-check your total frequency in the denominator - it's the most common place to make mistakes!
The process stays the same: multiply each mid-interval value by its frequency, add everything up, then divide by the total frequency. This gives you a good estimate of the mean for grouped data.