Im confused with the formulas VAR[f(x)] = a^2VAR(X + b) and Sum of Independent Random VAR(C) = VAR(A) + VAR(B)
-Adult males of a certain species of animal are known to have a mean weight of 1.3 kg with standard error of .2 kg.
Q: What is the standard error of the total weight of randomly selected groups of 4 males?
Now I have 2 solutions with different answers.
Using VAR[f(x)] = a^2VAR(X + b)
= 4^2 (.2^2)
= 0.64 kg
hence Standard error is 0.8 kg
Using VAR(C) = VAR(A) + VAR(B)
= .2^2 + .2^2 + .2^2 + .2^2
= 0.16 kg
hence Standard error is 0.4 kg
Which one is right?
If its not much to ask, could you give me a link to help me with this?
How do we choose the constant?