Question

The length of a phone conversation is normally distributed with a mean of 4 minutes and a standard deviation of 0.6 minutes.

What is the probability that a conversation lasts longer than 5 minutes?

0.54746
0.45254
0.04746
0.95254

Answer 1

calculate the z-score for the value of 5 minutes

z-score formula:

\[z = \frac{ x-μ }{ σ }\]
where x is the value being tested (5 minutes), μ is the mean (4 minutes) and σ is the standard deviation (0.6 minutes)

after you evaluate z, find the corresponding probability using either a z-table or a calculator

Answer 2

*need to add something, sorry:

when you calculate the z-score and find the probability, this is the probability that any random event will be *less than* the x-value. in this case, since we want the probability of getting *more than* 5 minutes, take (1 - the probability from the previous step)