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Given the following information about the production and demand of a commodity.
Obtain the two regression lines:
ADVERTISEMENT (x) (₹ in lakhs) 
DEMAND (y) (₹ in lakhs) 

Mean  10  90 
Variance  9  144 
Coefficient of correlation between x and y is 0.8.
What should be the advertising budget if the company wants to attain the sales target of ₹ 150 lakhs?
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Solution
Given, `bar(x)` = 10, `bar(y)` = 90, `sigma_x^2` = 9, `sigma_y^2` = 144, r = 0.8
∴ `sigma_x` = 3, `sigma_y` = 12
b_{yx} = `"r" sigma_y/sigma_x = 0.8 xx 12/3` = 0.8 × 4 = 3.2
b_{xy} = `"r" sigma_x/sigma_y = 0.8 xx 3/12` = 0.8 × 0.25 = 0.2
The regression equation of Y on X is
`("Y"  bary) = "b"_(yx) ("X"  barx)`
∴ (Y – 90) = 3.2 (X – 10)
∴ Y – 90 = 3.2 X – 32
∴ Y = 3.2 X – 32 + 90
∴ Y = 3.2 X + 58 ......(i)
The regression equation of X on Y is
`("X"  barx) = "b"_(xy) ("Y"  bary)`
∴ (X – 10) = 0.2 (Y – 90)
∴ X – 10 = 0.2 Y – 18
∴ X = 0.2 Y – 18 + 10
∴ X = 0.2 Y – 8 ......(ii)
When the company wants to attain the sales target of ₹ 150 lakhs,
Put Y = 150 lakh in equation (ii)
∴ X = 0.2 × 150 – 8 = 30 – 8 = 22
∴ The advertising budget should be ₹ 22 lakhs if the company wants to attain the sales target of ₹ 150 lakhs.
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