VIL—AVERAGES. 111
in another column (4). The positive and negative products are
totalled separately, giving totals — 776 and +509 respectively,
whence 3(f.£) = —267. Dividing this by #, viz. 632, we have
the difference of Jf from 4 in class-intervals, viz. 0-42 intervals,
that is 0-21 per cent. Hence the mean is 35-021 =3-29
per cent.
CALCULATION OF THE MEAN: Example i.—Calculation of the Arithmetic
Mean of the Percentages of the Population in receipt of Relief, from the
Figures of Table VIII, Chap. VI., p. 93.
(1) - (3) (4)
Mid-values
of the Deviation
Class-intervals ~~ Frequency from Arbitrary Product
{Percentage in Value 4 JE.
receipt of
Relief).
1 18 - 9d 90
5 48 - 4 192
2 J 72 - & 216
25 89 - 2 178
3 100 - 1 100
35 an =77sD
1 75
45 120
5 120
55 84
Zz 5 '
65 :
/
7°5
85
Total g = + 909 :
=(f2)= +509 - 776 = — 267
M-4=- - class-intervals= — 0°42 class-intervals
= — 0°21 units
-*. mean M=3'5-0'21= 3°29 per cent.
It must always be remembered that 3(f.£)/N gives the value of
M— 4 in class-intervals, and must not be added directly to 4
unless the interval is also a unit. In the present illustration the

(2)
-
43% .