JB Statistics

Question 1

mean

Answer 1

sum of terms / number of terms

Question 2

average of numbers in AP

Answer 2

(first + last) / 2
or
[ 2a + (n-1)d ] / 2

Question 3

weighted avg formula
two groups have weights = x & y
two groups have avg = p & q

Answer 3

( px + qy ) / x + y

Question 4

median(for odd number of terms) =

Answer 4

middle term = (n+1)/2 TH term

Question 5

median(for even number of terms) =

Answer 5

avg of two middle terms = n/2 TH and (n/2) + 1 TH term

Question 6

median of numbers in AP

Answer 6

(first + last) / 2
or
[ 2a + (n-1)d ] / 2

Question 7

relation b/w median and mean for numbers in AP

Answer 7

median = mean

Question 8

mode

Answer 8

term with max frequency

Question 9

Range

Answer 9

max value - min value

Question 10

Standard deviation =

Answer 10

√ ( { [ x1-x(avg)]^2 + [x2-x(avg)]^2 +…+ [xn-x(avg)]^2 } / n )

Question 11

Variance =

Answer 11

{ [ x1-x(avg)]^2 + [x2-x(avg)]^2 +…+ [xn-x(avg)]^2 } / n

Question 12

Relation b/w standard deviation & Variance

Answer 12

Variance = ( S.D. ) ^ 2

Question 13

Relation b/w SD and Range

Answer 13

SD<= range/2

Question 14

Normal distribution with:
m = mean
d = standard deviation

Another term - symmetric around the mean

Answer 14

Positive side of bell curve = 50%
m to m+d = 34%
m+d to m+2d = 14%
> m+2d = 2%

Negative side of bell curve = 50%
m to m-d = 34%
m+d to m-2d = 14%
< m-2d = 2%