1
JEE Main 2021 (Online) 25th July Evening Shift
+4
-1
The first of the two samples in a group has 100 items with mean 15 and standard deviation 3. If the whole group has 250 items with mean 15.6 and standard deviation $$\sqrt {13.44}$$, then the standard deviation of the second sample is :
A
8
B
6
C
4
D
5
2
JEE Main 2021 (Online) 20th July Evening Shift
+4
-1
If the mean and variance of six observations 7, 10, 11, 15, a, b are 10 and $${{20} \over 3}$$, respectively, then the value of | a $$-$$ b | is equal to :
A
9
B
11
C
7
D
1
3
JEE Main 2021 (Online) 20th July Morning Shift
+4
-1
The mean of 6 distinct observations is 6.5 and their variance is 10.25. If 4 out of 6 observations are 2, 4, 5 and 7, then the remaining two observations are :
A
10, 11
B
3, 18
C
8, 13
D
1, 20
4
JEE Main 2021 (Online) 18th March Evening Shift
+4
-1
Let in a series of 2n observations, half of them are equal to a and remaining half are equal to $$-$$a. Also by adding a constant b in each of these observations, the mean and standard deviation of new set become 5 and 20, respectively. Then the value of a2 + b2 is equal to :
A
425
B
250
C
925
D
650
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