Question

Facespace is a popular form of social media. Recent reports

show that the mean time spent on Facespace is 40 minutes a

day with a standard deviation of 6 minutes a day. The data is

normally distributed.

If 3900 people are on in one sitting, how many of them lie

within one standard deviation below the mean and

two standard deviations above the mean?

Answer 1

3192 persons! ✔️

Explanation:

From the statement, we know that μ = 40 [minutes] and σ = 6 [minutes]

There are 3900 people. And we need to find how many of the lie within one standard deviation below the mean and two standard deviations above the mean.

We need to find the probability between: 34 minutes and 52 minutes. With the help of a calculator we get that the probability is: P(34<z<52) = 0.8186

Therefore, 0.8186×3900 = 3192 persons! ✔️