Question

The mean number of hours per day spent on the phone, according to a national survey, is four hours, with a standard deviation of two hours. If each time was increased by one hour, what would be the new mean and standard deviation? (2 points)
Select one:
a. 4, 2
b. 4, 3
c. 5, 2
d. 5, 3

Answer 1

Answer:

The new mean is 5.

The new standard deviation is also 2.

Step-by-step explanation:

Let the sample space of hours be as follows, S = {x₁, x₂, x₃...xₙ}

The mean of this sample is 4. That is,$\bar x=\frac{x_{1}+x_{2}+x_{3}+...+x_{n}}{n}=4$

The standard deviation of this sample is 2. That is, $s=\frac{1}{n-1}\sum (x_{i}-\bar x)^{2}=2$.

Now it is stated that each of the sample values was increased by 1 hour.

The new sample is: S = {x₁ + 1, x₂ + 1, x₃ + 1...xₙ + 1}

Compute the mean of this sample as follows:

$\bar x_{N}=\frac{x_{1}+1+x_{2}+1+x_{3}+1+...+x_{n}+1}{n}\\=\frac{(x_{1}+x_{2}+x_{3}+...+x_{n})}{n}+\frac{(1+1+1+...n\ times)}{n}\\=\bar x+1\\=4+1\\=5$

The new mean is 5.

Compute the standard deviation of this sample as follows:

$s_{N}=\frac{1}{n-1}\sum (x_{i}-\bar x)^{2}\\=\frac{1}{n-1}\sum ((x_{i}+1)-(\bar x+1))^{2}\\=\frac{1}{n-1}\sum (x_{i}+1-\bar x-1)^{2}\\=\frac{1}{n-1}\sum (x_{i}-\bar x)^{2}\\=s$

The new standard deviation is also 2.