Answer:
n=4
Step-by-step explanation:
Given equation: \[\frac{1}{n-4}-\frac{2}{n}=\frac{3}{4-n}\]
Simplifying the Left Hand Side of the equation by taking the LCM of the denominator terms:
\[\frac{n}{n*(n-4)}-\frac{2*(n-4)}{n*(n-4)}=\frac{3}{4-n}\]
=> \[\frac{n - 2*(n-4)}{n*(n-4)}=\frac{3}{4-n}\]
=> \[\frac{n - 2n + 8}{n*(n-4)}=\frac{3}{4-n}\]
=> \[\frac{8 - n}{n*(n-4)}=\frac{3}{4-n}\]
=> \[(8-n)*(4-n) =n*(n-4)*3\]
=> \[n-8 =3n\]
=> \[2n =8\]
=> n = 4
The confidence interval would be (10.44, 12.16). This means that if we take repeated samples, the true mean lies in 90% of these intervals.
To find the confidence interval, we use:

We first find the z-value associated with this. To do this:
Convert 90% to a decimal: 90% = 90/100 = 0.9
Subtract from 1: 1-0.9 = 0.1
Divide by 2: 0.1/2 = 0.05
Subtract from 1: 1-0.05 = 0.95
Using a z-table (http://www.z-table.com) we see that this is directly between two z-scores, 1.64 and 1.65; we will use 1.645:
The answer is B 113.04
Explanation
Assuming pi in this instance is 3.14
The formula for the area of a circle is A=(pi)r^2
Plug in the radius
A=3.14x6^2
Is 113.04
The correct answer to 820/42= 19.52 (rounded answer would be 20). I hope I helped :)