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Consider the following data

Year (x)201420162018202020222024
Profit (in Rs. Thousand) (y)7910121414

Then for the above data the equation of straight line trend by method of least square is given by:

Solution

✅ Correct Option: 3

The task is to find the equation of a straight line that best fits the given profit data using the method of least squares.


Using a change of variable to simplify calculations with large year values.

Let u=x−2019u = x - 2019

Year (x)u = x - 2019Profit (y)
2014-57
2016-39
2018-110
2020112
2022314
2024514

Calculate the required sums:

n=6n = 6

∑u=−5+(−3)+(−1)+1+3+5=0\sum u = -5 + (-3) + (-1) + 1 + 3 + 5 = 0

∑y=7+9+10+12+14+14=66\sum y = 7 + 9 + 10 + 12 + 14 + 14 = 66

∑u2=25+9+1+1+9+25=70\sum u^2 = 25 + 9 + 1 + 1 + 9 + 25 = 70

∑uy=(−5×7)+(−3×9)+(−1×10)+(1×12)+(3×14)+(5×14)\sum uy = (-5 \times 7) + (-3 \times 9) + (-1 \times 10) + (1 \times 12) + (3 \times 14) + (5 \times 14)

∑uy=−35−27−10+12+42+70=52\sum uy = -35 - 27 - 10 + 12 + 42 + 70 = 52


The equation of the line is y=a+buy = a + bu

Since ∑u=0\sum u = 0:

b=∑uy∑u2b = \dfrac{\sum uy}{\sum u^2}

b=5270b = \dfrac{52}{70}

b=2635b = \dfrac{26}{35}


a=∑yna = \dfrac{\sum y}{n}

a=666a = \dfrac{66}{6}

a=11a = 11


The equation becomes:

y=11+2635uy = 11 + \dfrac{26}{35}u

Substituting u=x−2019u = x - 2019:

y=11+2635(x−2019)y = 11 + \dfrac{26}{35}(x - 2019)


35y=385+26(x−2019)35y = 385 + 26(x - 2019)

35y=26(x−2019)+38535y = 26(x - 2019) + 385

Therefore, the equation of straight line trend is 35y=26(x−2019)+38535y = 26(x - 2019) + 385

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