Question
Find arithmetic mean from the following data using step-deviation method:
Temperature (°C)
-40 to -30
-30 to -20
-20 to -10
-10 to 0
0 to 10
10 to 20
20 to 30
No. of Days
10
28
30
42
65
180
10

Answer

C.I.
f
M.V. (m)
dx
dx'
fdx'
-40 to -30
10
-35
-30
-3
-30
-30 to -20
28
-25
-20
-2
-56
-20 to -10
30
-15
-10
-1
-30
-10 to 0
42
-5
0
0
0
0 to 10
65
5
0
0
0
10 to 20
180
15
10
1
180
20 to 30
10
25
20
2
20
 
$\Sigma\text{f}=365$
 
 
 
$\Sigma\text{fdx}'=84$
$\overline{\text{X}}=\text{A}+\frac{\Sigma\text{fdx}'}{\Sigma\text{f}}\times\text{i}$
$=5-\frac{84}{365}\times10$
$=5-.23\times10$
$=5-2.3$
$=2.7$

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