1. ©2009 – Not to be sold/Free to use
Stage 4
Year 9
Grouped Data
Grouped Data
Mean
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©2009 – Not to be sold/Free to use

2. Grouped Data In grouped data: Data classes must not overlap.
Intervals must be of equal size.
They are used for a large range of scores.
A class centre (cc) is calculated by averaging the end points.

3. Finding the Mean using Σ
Score x
Tally
Freq fx f 1 2 3 4 5
Σf =
Σfx =
Σfx Σf
x = x x 3
1x3 3 66 22 =
Mean x 4
2x4 8 x 7
3x7 21
= 3 x 6
4x6 24 2
5x2 10
Σ means
‘Sum’ or Add Up 22 66 3

4. Grouped Data – The Mean Class Class Centre cc Tally f f.cc 0-4 2
(0+4)÷2 2
2x2 4
Σf.cc Σf
x =
5-9
(5+9)÷2 7 3
7x3 21
10-14
(10+14)÷2 12 1
12x1 12
380 20 =
15-19
(15+19)÷2 17 4
17x4 68
20-24
(20+24)÷2 22 3
22x3 66
= 19
25-29
(25+29)÷2 27 4
108
27x4
30-34
(30+34)÷2 32 2
32x2 64 1
37x1 37
35-40
(35+40)÷2 37
Σf= 20
Σf.cc=
380