# Stats question , have work and answer shown

1. Nov 6, 2008

### deaky220

1. The problem statement, all variables and given/known data

i didnt know which forum stats is posted in so i posted it here, but the problem says the q is , Sheilas measure glucose level one hour after a sugary drink varies according to the normal distribution (u= 125 mg/dl) and r=10 mg/dl. What is the level L such that there is a probability only 0.05 that the mean glucose level of 4 test results falls above L?

2. Relevant equations

x= u(mew) + z*r

3. The attempt at a solution
I did a backwards normal calculation of x= 125 + .5199 (from table A probs) * 10 = 130.199

i think its right but i dunno, does the 4 play a part in my equation or is this the wrong way to do it? ANY information would be helpful

2. Nov 6, 2008

### HallsofIvy

Staff Emeritus
Yes, it does. The average of n samples from a population with mean $mu$ and standard deviation $\sigma$ is normally distributed with mean $mu$ and standard deviation $\sigma\sqrt{n}$. Notice that means that the larger sample you have the smaller its standard deviation is and the more "accurate" it is.