What summary statistics do you have for the groups?

The overall mean is a weighted average of the group means.
DEVSQ(groups1&2) =
DEVSQ(group1)+DEVSQ(group2)+(AVERAGE(group1)-AVERAGE(group2))^2*COUNT(group1)*COUNT(group2)/(COUNT(group1)+COUNT(group2))

Jerry

"Ina" wrote:

i don't know how to find standard deviation for grouped data. this is for my
add maths project. pls help me. explain to me step-by-step coz i really don't
have a clue how to find it using excel. thnx.