statistics

Question

Set no. :- 1,  2 , 3

no.of data:- 9 ,12 , 15

 mean value :- 8 , 7 , 9

 standard deviation:- 1.6 , 1.2 , 1.4 

Considering all the data sets together , the overall men value will be 

a) 7.24

b) 7.66

c) 0.08

d)0.05

Answer 1

mean = (-8x9 + 7x12 + 9x15)/n

= (-72+84+135)/n

= 146/(9+12+15)

= 146/36 =

=73/18

= about 4.06

all the options are wrong

but had -8 been a +8 then a) or b) would be closest

then mean = ((72 +84 + 135)/36 = 291/36 = 97/12 = about 8.08

still all the options are wrong