112 THEORY OF STATISTICS. 
interval is half a unit, and accordingly the quotient 267/632 is 
halved in order to obtain an answer in units. Care must also be 
taken to give the right sign to the quotient. 
10. As the process is an important one we give a second illustra- 
tion from the figures of Table VI., Chap. VI. In this case the class- 
interval is a unit (1 inch), so the value of M — A is given directly 
by dividing 3(f.£) by &V. The student must notice that, measures 
having been made to the nearest eighth of an inch, the mid-values 
of the intervals are 577, 587, ete., and not 57-5, 58-5, ete. 
CALCULATION OF THE MEAN: Example il.— Calculation of the Arithmetic 
Mean Stature of Male Adults in thé British Isles from the Figures of 
Chap. VI., Table VI, p. 88. 
(1) £2) (3) (4) 
Deviation 
Height, Frequency from Arbitrary Product 
Inches. ie Value 4 JE. 
: 
57- 2 -10 20 
58 4 - 9 36 
59— 14 ~ 8 | 112 
60—- 41 - 17 : 287 
61- 83 = 498 
62— 169 - 845 
63- 394 —- 1576 
64— 669 - 2007 
65— 990 —- 2 1980 
66— 1223 - 1 1223 
67—- 1329 0 — 8584 
68— 1230 +1 1230 
69— 1063 + 2 2126 
70- 646 + 3 1938 
71- 392 + 4 1568 
72—- 202 + 5 1010 
75%— 79 + u 474 
74— ad + 7 224 
75- 15 + °C 128 
76— Fo 45 
77- 10 20 
Total & n + 8763 
2(ft)= +8763 —8584= + 179 
wer : 
M—-A4= + orgs = + 02 class-intervals or inches. 
.% M=67{+'02=6746 inches. 
(a 
B&F