If the arithmetic mean of the data given below is 28, then find out the missing frequency.
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Answers
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Answer
Let the missing frequency be x
X Frequency(f) Mid value (m) fm
0-10 12 5 60
10-20 18 15 270
20-30 27 25 675
30-40 x 35 35(x)
40-50 17 45 765
50-60 6 55 330
Σf = 80+x Σfm = 2100+35 x
∴ Mean = Σfm / Σf
Mean is given 28
Now
=> 28 = 2100+35 f / 80+x
=> 28(80+x = 2100+35 x
=> 2240 + 28 x = 2100+35 x
=> 2240-2100 = 35 x -28 x
=> 120 = 7 x
=> x = 120/7
=> x = 20