X²-9x=36
minus 36 both sides
x²-9x-36=0
what 2 numbers multiply to -36 and add to -9
-12 and 3
(x-12)(x+3)=0
set to zero
x-12=0
x=12
x+3=0
x=-3
the number is either -3 or 12
Answer:


The confidence interval of standard deviation is:
to 
Step-by-step explanation:
Given

See attachment for the formatted data
Solving (a): The mean
This is calculated as:

So, we have:




Solving (b): The standard deviation
This is calculated as:




--- approximated
Solving (c): 95% confidence interval of standard deviation
We have:

So:



Calculate the degree of freedom (df)



Determine the critical value at row
and columns
and 
So, we have:
---- at 
--- at 
So, the confidence interval of the standard deviation is:
to 
to 
to 
to 