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Find the mean of each of the following frequency distributions:

 Class interval:  50 - 70  70 - 90  90 - 110  110 - 130  130 - 150  150 - 170
 Frequency:  18  12  13   27  8  22

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Let the assumed mean (A) be 100.

 Class interval  Mid value (xi)  di = xi - 100  ui\(\frac{xi-100}{20}\)  fi  fiui
 50 - 70  60 -40 -2 18 -36
 70 - 90  80 -20 -1 12 -12
 90 - 110 100 0 0 13 0
 110 - 130  120 20 1 27 27
 130 - 150  140 40 2 8 16
 150 - 170  160 60 3 22 66
   N = 100 \(\sum\)fiui = 61

A = 100, h = 20

Mean = A + h x \(\frac{\sum f_iu_i}{N}\)

\(=100+20\times\frac{61}{100}\)

\(=100\,+12.2\)

\(=112.2\)

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