©2009 – Not to be sold/Free to use Stage 4 Year 9 Grouped Data Grouped Data Mean Press Ctrl-A ©2009 – Not to be sold/Free to use

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.

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

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