Consider the following problem:
Here is my attempt:
The total perimeter is: $$231.8\times80=18544$$ Of this perimeter $$\frac{18544}{1+\sqrt2}$$ Contributes to the total width. As each poster contains 2 widths the mean width is the above divided by 160. Hence the mean width is 48.0. The variance is the mean of the squares minus the square of the mean. Standard deviation is the root of this.
Hence the standard deviation should be the following:
$$\sqrt{\frac{200120}{160}-48.0^2}$$
However, the radicand is unfortunately negative. The answers state that the standard deviation is 14.0. When dividing 200120 by 80 instead of 160, the answer yields 14.0. Yet, I cannot understand why I would divide by 80 rather than 160.
How would you solve this problem?