Explanation
Givenbxy=0.2byx=0.8r=√bxy×byxr=√0.36r=0.6
Where r is coefficient of correlation.
Correlation coefficients are expressed as values between 1 and +1. A coefficient of +1 indicates a perfect positive correlation: A change in the value of one variable will predict a change in the same direction in the second variable. A coefficient of 1 indicates a perfect negative correlation: A change in the value of one variable predicts a change in the opposite direction in the second variable. Hence, correct answer is option C.
Physics(P)
Mathematics (M)
Rank (P)
|d|
d2
98
60
72
62
56
40
39
52
30
78
65
70
38
54
32
31
6
3
1
2
4
7
8
5
9
0
n=9,∑d2=40
r=1−6∑d2n(n2−1)=1−40×69(92−1)=1−240720=0.66
Since r>0 we can say that this indicate a moderate positive relationship between marks of physics and mathematics.
Marks of Physics (X)
Marks in Maths(Y)
XY
X2
Y2
35
23
47
17
10
43
28
33
45
49
12
1050
759
2115
391
80
2107
108
24
868
1225
529
2209
289
100
1849
81
784
900
1089
2025
64
2401
144
16
961
∑X=218,∑Y=235,∑XY=7502,∑X2=7102,∑Y2=8129
N=09
Cov(x,y)=∑XYN−∑XN.∑YN=750209−2189.2359=201.08
σx=√∑X2N−(∑X2N)2=√710209−(21809)2=14.22
σy=√∑Y2N−(∑Y2N)2=√812909−(2359)2=14.88
r=Cov(x,y)σx.σy=201.0814.22×14.88=0..95
Competition
1st Judge
Rank
2nd Judge
A
B
C
D
E
5.7
5.8
5.9
5.6
5.5
6.0
n=5,∑d2=12
r=1−6∑d2n(n2−1)=1−6×125(52−1)=1−72240=0.44
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