The first step is to find the midpoint for each interval
Midpoint = (lower limit + upper limit)/2
For 40 to 44,
midpoint = (40 + 44)/2 = 42
We would apply the same formula for the other intervals
The table is shown below
Interval Frequency(f) midpoint(x) fx
40 - 44 2 42 84
45 - 49 5 47 235
50 - 54 13 52 676
55 - 59 7 57 399
60 - 64 3 62 186
Mean = Σfx/Σf
Σfx = 84 + 235 + 676 + 399 + 186 = 1580
Σf = 2 + 5 + 13 + 7 + 3 = 30
Mean = 1580/30
Mean = 52.7
