Question

the mean of 10 observation is 9.8 and mean of 25 observations is 13. calculate the mean of all 35 observations taken together

Answer 1

Mean of 10 observations =9.8
sum of observations=10*9.8
=98
Mean of 25 observations=13
sum of observations=25*13
=325

now mean of 35 observations=(325+98)/35
=423/35
=12.08571429

Answer 2

let mean of 10 be m1
that of 25 be m2
m1 of 10 = 9.8
So sum = 9.8×10 = 98
m2 of 25 = 13
Sum = 25×13= 325
total sum of 10+25=325+98

total sum of 35= 423
total mean of 35 = 423÷35 = 12.08