# standarddeviation

1. ### Exercise on standard distribution

Hello, Suppose I want to calculate the probability for a user to pass from a basic to a premium account within the end of Q1 (i.e. end of march). I know that this is distributed with mean=50 days and st.dev=10 days, then the probability that a user pass to a premium account within the end of...
2. ### Working out standard deviation for three random variables with different sized ranges

X = {1,2,3,4,5,6}, Y = {1,2,3,4}, Z = {2,4,6,8}. The question is: work out standard deviation of A = 2S-1, where S = the sum of the three random variables. I know that E(X) = 3.5, E(Y) = 2.5, E(Z) = 5 Var(X) = 2.916, Var(Y) 1.25, Var(Z) = 5 Now in order to find out the standard...
3. ### Help with errors in a research

Hi all, I am new to this forum and I am really glad that I found it. Hope I'll be able to offer some help as well. My problem is fairly simple, but I couldn't find the answer anywhere and my attempts were very poor. I am doing analyses on some soil samples and I am getting an analytical...
4. ### Stupid question: deriving standard dev from mean, C.I., and sample size

So I'm trying to get a standard deviation value for a table of statistics that includes a mean, a 95% confidence interval, and a sample size. I am actually unsure if the sample size is correct, more on that later. It's been a while since I've taken statistics and attempting to research this...