NCERT Class XI Mathematics - Statistics - Solutions
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Question : 29
Total: 34
The mean and variance of 7 observations are 8 and 16, respectively. If five of the observations are 2, 4, 10, 12, 14. Find the remaining two observations.
Solution:
SLet the remaining two observations be x and y. Then we are given that
= 8
⇒ 42 + x + y = 56 ⇒ x + y = 14 ... (i)
Also ,
( 2 2 + 4 2 + 10 + 12 2 + 14 2 + x 2 + y 2 ) − ( 8 ) 2 = 16
⇒
( 4 + 16 + 100 + 144 + 196 + x 2 + y 2 ) − 64 = 16
⇒ 460 +x 2 + y 2 = 560 ⇒ x 2 + y 2 = 100 ... (ii)
Now( x + y ) 2 + ( x – y ) 2 = 2 ( x 2 + y 2 )
⇒( 14 ) 2 + ( x – y ) 2 = 2 × 100 [Using (i) & (ii)]
⇒( x – y ) 2 = 200 – 196 ⇒ ( x – y ) 2 = 4 ⇒ x – y = ± 2
When x – y = 2 and x + y = 14, we get x = 8 and y = 6
When x – y = –2 and x + y = 14 we get x = 6 and y = 8.
So, the remaining two observations are 6 and 8.
⇒ 42 + x + y = 56 ⇒ x + y = 14 ... (i)
Also ,
⇒
⇒ 460 +
Now
⇒
⇒
When x – y = 2 and x + y = 14, we get x = 8 and y = 6
When x – y = –2 and x + y = 14 we get x = 6 and y = 8.
So, the remaining two observations are 6 and 8.
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