1
JEE Main 2020 (Online) 8th January Morning Slot
+4
-1
The mean and the standard deviation (s.d.) of 10 observations are 20 and 2 resepectively. Each of these 10 observations is multiplied by p and then reduced by q, where p $$\ne$$ 0 and q $$\ne$$ 0. If the new mean and new s.d. become half of their original values, then q is equal to
A
10
B
-20
C
-10
D
-5
2
JEE Main 2019 (Online) 12th April Morning Slot
+4
-1
If the data x1, x2,......., x10 is such that the mean of first four of these is 11, the mean of the remaining six is 16 and the sum of squares of all of these is 2,000 ; then the standard deviation of this data is :
A
$$\sqrt 2$$
B
2
C
2$$\sqrt 2$$
D
4
3
JEE Main 2019 (Online) 10th April Evening Slot
+4
-1
If both the mean and the standard deviation of 50 observations x1, x2,..., x50 are equal to 16, then the mean of (x1 – 4)2 , (x2 – 4)2 ,....., (x50 – 4)2 is :
A
400
B
480
C
380
D
525
4
JEE Main 2019 (Online) 10th April Morning Slot
+4
-1
If for some x $$\in$$ R, the frequency distribution of the marks obtained by 20 students in a test is :

Marks 2 3 5 7
Frequency (x + 1)2 2x - 5 x2 - 3x x

then the mean of the marks is
A
3.0
B
2.8
C
2.5
D
3.2
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