Answer:
a. 
b. 
c. 
Explanation:
a) The average of this values is the sum each number divided by the total number of values.

is values of each diameter- N is the total number of values. N=6


b) The standard deviation equations is:

If we put all this values in that equation we will get:

Then the mean diameter will be:
c) We know that the density is the mass divided by the volume (ρ = m/V)
and we know that the volume of a cylinder is: 
Then:

Using the values that we have, we can calculate the value of density:

We need to use propagation of error to find the error of the density.
- δm is the error of the mass value.
- δd is the error of the diameter value.
- δh is the error of the length value.
Let's find each partial derivative:
1. 
2. 
3. 
Therefore:


So the density is:

I hope it helps you!