Q26 / 77 · NTA Abhyas (JEE Main) 2020 · Mathematics · Statistics

If both the mean and the standard deviation of 50 observations x1, x2, …, x50 are equal to 16, then the mean of x1-42, x2-42, …,x50-42 is

  • A
    525
  • B
    480
  • Correct answer
    C
    400
  • D
    380

Solution

For observations x1, x2, ...........x50
Mean, x-=∑xi 50=16 . . . . . (i)
Variance, σ2=∑xi250-(x-)2=162
⇒∑xi250=162+(x-)2=162+162=512 . . . . . (ii)
So, the mean value of (x1-4)2, (x2-4)2, .......(x50-4)2 will be
=∑(xi-4)250=∑xi2-8∑xi+16×5050
=∑xi250-8∑xi50+16=512-8×16+16=400 (using (i) and (ii))

Hence, the correct answer is option: 'C'.

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